Access to this full-text is provided by Springer Nature.
Content available from Clean Technologies and Environmental Policy
This content is subject to copyright. Terms and conditions apply.
Vol.:(0123456789)
1 3
Clean Technologies and Environmental Policy (2024) 26:45–65
https://doi.org/10.1007/s10098-023-02579-z
ORIGINAL PAPER
A conceptual model foracircular city: acase study ofMaribor,
Slovenia
KristijanBrglez1,2· MatjažPerc1,3,4,5· RebekaKovačičLukman1,2
Received: 14 February 2023 / Accepted: 9 July 2023 / Published online: 29 July 2023
© The Author(s) 2023
Abstract
Cities play a crucial role in achieving sustainable development. Decision-makers require assistance in developing city trans-
formation plans amidst the emergence of various city models. A content analysis using concept mapping was conducted to
examine smart, circular, and green city models. The analysis, supported by Leximancer, revealed that city models are evolving
by adopting beneficial solutions from competitors, reflecting a strong focus on sustainable development. Additionally, twenty-
four research areas essential for implementing a circular city were identified and validated. Furthermore, a conceptual model
for a circular city was developed, incorporating the Define-Measure-Analyse-Improve-Control tool and a problem-solving
system. Testing the model on Maribor highlighted challenges in monitoring the transition towards circularity. The study
validates the established model but emphasises the need for further research and case studies to verify its practicality. This
scientific research enhances the understanding of city models and their evolution towards sustainability, providing valuable
insights for decision-makers and urban planners.
Graphical abstract
Keywords City models· Conceptual model· Define-Measure-Analyse-Improve-Control Process· Content analysis·
Problem-solving structure
Extended author information available on the last page of the article
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
46 K.Brglez et al.
1 3
Introduction
By 2019 over 55% of the global population resided in urban
areas (United Nations 2019). With their hindsight areas, cit-
ies consume over 60% of global energy and over 75% of
the planet’s material resources (Dodman etal. 2017; World
Economic Forum 2022). Such consumption rates generate
an increased impact on the environment and society. Thus,
cities are responsible for producing up to 50% of global
solid waste and 70% of greenhouse emissions yearly (OECD
2021). Projections by Gao and O’Neill (2020) indicate an
increase in urban areas by 1.8 to 3.6 by 2100 in comparison
with the year 2000, with the residing population expected
to rise by 15 per cent, according to United Nations (2019),
while World Economic Forum (2022) projecting 80% of
global population residing in urban areas by the year 2050.
The increased growth of cities and their population presents
a unique challenge for policymakers, researchers, experts,
and society in achieving sustainable development in cities.
The importance of cities in combating rising economic,
social, and environmental issues has not gone unnoticed. The
United Nations emphasised the cities as an important area
to be considered, thus including them under the 11th goal
of Sustainable cities and communities (General Assembly
UN 2015). European Union (EU) delivered a renewed Urban
Agenda for the EU (Urban Agenda for the EU 2023), further
supporting countries' dedication towards sustainable devel-
opment in urban areas. Such directives have fostered the
development of various city models (smart, green, sustain-
able cities), including circular cities, encompassing circular
economy principles for urban areas. The circular city model
was supported by the EU's "Circular cities and regions ini-
tiative” to reduce pressure on natural resource consumption
and create sustainable and circular jobs (European Commis-
sion 2022). The initiative adopted the European Green Deal
(European Commission 2021) and the Urban Agenda for the
EU (Urban Agenda for the EU 2023).
The emergence of various city models for urban areas
poses a challenge for decision-makers, experts, and research-
ers. However, there is a distinction in tackling acceleration
towards a sustainable city for various city models. According
to the existing literature review, we can perceive the preva-
lent features of the mentioned city's models. For example,
smart cities employ smart and digital technologies (Moradi
2020; Tiware etal. 2021), circular cities introduce princi-
ples of circular economy from the strategic and practical
perspectives (Crippa etal. 2022), while green cities focus on
greening public spaces (Jia etal. 2021; Zhang etal. 2022).
City models’ reviews are beneficial for furthering the city's
development. However, the rapid rise of publicised review
papers presents an obstacle between discerning potential
breakthroughs or rewriting published findings (Nature
Sustainability 2021). Understanding city models' underly-
ing fields and potential overlaps can forward implementing
beneficial ideas in practice.
In recent years, there has been a tendency towards the
circular economy and subsequent implementation in urban
areas (European Commission 2015; European Commission
2019). The circular economy implementation within cities
faced several barriers, as the circular economy was primarily
developed for industry and services (Williams 2019), includ-
ing product development (Boeri etal. 2019). The transition
towards redefining the circular city model as a built or urban
environment has begun with increased research and support
by organisations such as the EU, Ellen MacArthur Founda-
tion, and the UN (Murray etal. 2017). A transformation of
the established circular economy approach to better accom-
modate the intricate systems presented by cities is needed
(Prendeville etal. 2018). The increased interest in circular
cities spurred the development of several research areas,
such as building on resource efficiency (Ness and Xing
2017), circularity in port cities (Gravaguolo etal. 2019;
Cerreta etal. 2020), establishing circular tools (Girard &
Nocca 2019), nexus for energy, food and transport (Paiho
etal. 2021). Cities are considered complex built systems,
and defining circularity models should consider a systems
approach (Wijkman etal. 2019). Systems approach in cities
were perceived in the "ReSOLVE” approach (Prendeville
etal. 2018), complex urban system structure (Rios etal.
2022), and inclusion of resilience hubs across urban sys-
tems (Boeri etal. 2019). However, these models focused
more on various areas (e.g. energy, waste, food sector), not
comprehending the entire system. Also, statistical validation
and a transition measurement system are needed to provide
adequate information for decision-makers. Inspired by the
existing studies and research the main challenge is not a
circular approach implementation but measuring accelera-
tion towards circularity and providing continuous improve-
ments backed with statistical and reliable data (Birgovan
etal. 2022; Paoli etal. 2022). A solution can emphasise a
circular city model based on the Define-Measure-Analyse-
Implement-Control (DMAIC) tool and problem-solving
system, represented within this paper. The DMAIC tool, as
part of Six Sigma, is a data-driven technique that enables a
project-based approach, providing an established five-phase
structure, enabling the identification of possible solutions,
their development and implementation (Jamil etal. 2020).
Such an approach allows for semi- and final loops through-
out the process (Sokovic etal. 2010) and allows continuous
improvement to already implemented circular approaches
while enabling a system perspective. As this approach is data
and statistically-driven (Monday 2022), it enables manage-
ment through measurement techniques. It allows the promo-
tion of “state-of-the-art” maps before and after the imple-
mentation (de Mast and Lokkerbol 2012). Furthermore, it
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
47A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
coincides with the need for measuring systems for transi-
tioning from a linear to a circular economy (Birgovan etal.
2022; Paoli etal. 2022). The problem-solving structure
enables one to focus on the roots of issues (Mingers and
Brocklesby 1997). Engaging DMAIC and problem-solving
into one model assures a systemic structure supported by
measurement techniques and supports developing strategies
for the transition towards circularity.
Thus, the research focus has been given to the three main
areas. Firstly, to examine the extent of correlation in devel-
oping different city models, exploring their shared areas
of interest and the advantages of adopting an integrated
approach. This analysis has been conducted via a research
papers' content analysis on circular, green, and smart cities.
Then, to identify key research fields, crucial for the pro-
gression of circular cities and their transition from the cur-
rent linear strategies. Understanding the existing research
focus is essential in establishing a foundation for devising
strategies and projects that can guide policymakers when
incorporating circular activities. Third, to design and test
a conceptual model based on the DMAIC (Define, Meas-
ure, Analyse, Improve, Control) tool and a problem-solving
structure. This model incorporates the identified research
fields that promote circular growth. Through a case study,
strengths and potential shortcomings of the model are identi-
fied and addressed to enhance its effectiveness. This research
is essential as it can guide policymakers in formulating strat-
egies that facilitate continuous improvement of their cities
and lay the groundwork for possible unified standards in the
transformation towards a circular city.
Methods
This section represents a methodological approach and
methods, comprehending details on literature review and
content analysis, implementing and testing DMAIC process.
A visual presentation of our research is seen in Fig.1.
Content analysis
The search inquiry consisted of three separate searches
focused on various city models. The inquiry was conducted
in the Web of Science (WoS) Core Collection database,
which is well-maintained, valid and suitable for bibliometric
analysis (Pasko etal. 2021). The ten years were considered
(from 1st January 2012 to 31st December 2022) as a con-
tent analysis requires at least three years (Bornmann and
Leydesdorff 2014). Such a period also allows for examin-
ing the change in research trends along with strategic docu-
ments, such as the Agenda on Sustainable Development
Goals (United Nations 2013). Boolean operators used in the
inquiry are provided in Table1. Furthermore, we have con-
sidered only articles, review articles and proceeding papers
in English.
Fig. 1 A research methodology for designing and testing a conceptual model for circular cities
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
48 K.Brglez et al.
1 3
The identified papers for each inquiry were distributed
into three groups aligned with city models (smart, circu-
lar, green). A two-step screening procedure was applied,
enabling paper selection per a set of individual constraints
(Padilla-Rivera etal. 2020). The first step comprehended
an abstract and title overview, where we excluded papers
with no content links to the city models. The second step
comprised a content review, where at least one of the fol-
lowing factors had to be attained:
• the keywords needed to have a contextual meaning in the
paper’s content to the inquiry,
• the inclusion of other significant keywords closely related
to city models (e.g. smart technology, big data for the
smart city).
The initial inquiry and the two-step screening procedure
results are shown in Table2. The established database was
a basis for additional content and statistical analyses.
The content analysis was implemented using Lexi-
mancer software. Leximancer is a tool which uses text
mining to generate topic models or concepts based on high-
frequency words garnered from the text materials (Univer-
sity of Surrey 2022). The software performs analysis using
natural language text data (Biroscak etal. 2017) and apply-
ing the Bayesian-based algorithm (Smith and Humpreys
2006). Leximancer builds a concept system using thematic
and semantic inquiries (Smith 2003), grouped into themes
with associations and occurrences (Cretchley etal. 2010).
Leximancer visualises concepts, providing additional
information about interrelationships and the concept's
strength (Cretchley etal. 2010; Angus etal. 2013). Such
visualisation is achieved by representing themes as cir-
cles, with their colour differentiation building a heat map.
The warmer colours (e.g. red, orange) are representative
of prevalent themes, while the cooler colours (e.g. green,
blue) mark less significant themes (Engstrom etal. 2022).
The association by tags analysis enables additional data
representation. Tags are not directly involved by identi-
fied themes or concepts but are searched directly in the
provided publications, exploring existing data and analysis
avenues (Wilk etal. 2021). The tag's positioning within the
concept map, concerning the heat map, represents speci-
fied research areas of significance (Biesenthal and Wilden
2014), improving understanding regarding strong seman-
tic connections and overlaps between tags, concepts and
themes (Campbell etal. 2011; Wilk etal. 2021).
DMAIC model
Identified key concepts and emerging trends were used for
designing a DMAIC conceptualisation model, further imple-
mented in Maribor, Slovenia. DMAIC enabled a holistic and
systematic approach to process improvement and was mainly
used in enterprise or manufacturing sectors. However, its
employment was lately also observed in other sectors, such as
environmental management (Reid etal. 1999), IT technology
(Biesialska etal. 2018), and management of cities (Qayyum
etal. 2021). Its adaptability and flexibility due to the generic
method conception are advantageous when applied to dif-
ferent sectors (Sokovic etal. 2010). Including statistical and
measurement approaches is a valuable asset for DMAIC (de
Mast and Lokkerbol 2012). However, the DMAIC tool is yet to
entail environmental aspects, measurement systems that sup-
port sustainable development and integration of digital data
("big data"), increasing its competitiveness (Sony etal. 2020).
The DMAIC is commonly represented as a circular cycle con-
sisting of five stages with successive steps linked to at least
two other steps (Sokovic etal. 2010). The five steps consist of
(1) Defining the goal and its requirements, (2) Measuring the
Table 1 Boolean operators used
in the inquiry for city models City model Boolean operators
Circular city 1. (ALL = ("circular cit*" OR "circular town" OR "circular munici-
pality" OR "circular metropolis" OR "circular cosmopolis"))
AND ALL = (concept* OR defin* OR care OR model OR idea)
2. ((ALL = ("circular cit*" OR "circular town" OR "circular
municipality" OR "circular metropolis" OR "circular cosmopo-
lis"))) AND ALL = (indicat*)
Green city 1. ALL = (“green cit*”) AND ALL = (review AND concept*)
2. ALL = (“green cit*”) AND ALL = (definition OR concept*)
Smart city 1. ALL = ("smart city*") AND ALL = (review AND concept*)
2. ALL = (“smart city*”) AND ALL = (definition OR concept*)
Table 2 Inquiry and two-step screening procedure result for city
models
City model Initial search 1st step screen-
ing
2nd step
screen-
ing
Smart city 6995 768 436
Circular city 141 111 66
Green city 205 167 69
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
49A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
current process, (3) Analysing the results of measurements,
(4) Improvement of processes, implementation, and removal
of imperfections and (5) Control over-improved processes, and
constant monitoring (Pyzdek etal. 2010; Sony etal. 2020).
Such distribution enables a continuous and holistic approach
to either resolve or improve the current status.
Aside from the DMAIC tool, we incorporated the prob-
lem-structuring approach as a problem-solving option.
Unstructured challenges are characterised by multiple actors,
perspectives, conflicting interests, critical uncertainties, and
essential intangibles (Rosenhead & Mingers 2001). Consid-
ering cities' complexity, we can discern that any predica-
ments occurring within them has attributes related to one
of the characterisations above. Problem-solving allows us
to construct a holistic map and identify causes associated
with the challenge (Mingers & Brocklesby 1997; Chakra-
vorty etal. 2008). The problem-solving models must be con-
structed so that they can operate iteratively, can be easily
accessible to users with different knowledge backgrounds
and can be identified and implemented on a local scale (Min-
gers and Rosenhead 2004). We combined the 5S method
challenge identification, information gathering, generation
and evaluating solutions and implementation of the best
result (Chakravorty etal. 2008) with a systematic problem-
solving structure to create conceptual model.
When considering a city, it is vital to view it as a complex
living ecosystem. It is a natural counterpart and employs
many aspects of nature's circularity, such as metabolism,
with its distinct inputs (e.g. products) and outputs (e.g.
waste) (Golubiewski 2012). Such an approach enables us
to view the city from another standpoint, not as a human-
created system, but as a "living creature" that adheres to
the same laws as all living creatures, e.g. Lotkas maxi-
mum power principle (Ulgiati and Zucaro 2019). Nature,
without the interference of society, can be considered the
best-optimised closed loop with zero losses during multiple
Fig. 2 A model, based on guidelines questions and actions needed for implementing circular city's activities
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
50 K.Brglez et al.
1 3
iterations of its cycle (Long 2020) and creating closed-loop
systems (Kara etal. 2022). Closed loops prevent the loss
of vital resources (Wahlström etal. 2019), prolong their
use (Blomsma and Brennan 2017) and positively contrib-
ute towards the environment (Yang etal. 2022) and climate
change issues (Stefanakis etal. 2021). Considering the
DMAIC tool, promoting a circular approach to resolving
existing problems and a problem-solving structure approach,
we can theoretically achieve an artificial loop similar to
nature. A visualisation is represented in Fig.2.
It is crucial to consider areas in the city to readdress.
Cities are built systems with many subsystems referred to
as resource flows, energy production, infrastructure, and
society. Any potential solution for a subsystem needs to
reconsider possible changes to other subsystems related to
it (Johnson 2012). The conceptual model was divided into
the five steps of the DMAIC model, with an explanation
for the needed actions to complete it. The execution of the
model presented will enable a systematic approach and ease
future improvements to the city itself.
The Define phase is the initial phase of the DMAIC
method and is crucial when approaching the challenges
the city wants to address. Considering the problem-solving
structure, a systematic approach to identifying interesting
city areas is needed, with a basis on available data. Before
solution implementation, several mid-goals and actions are
needed such as (1) strategic approach creation, (2) con-
straints, (3) city holders, stakeholders, and other public
groups inclusion, and (4) value stream creation, which are
derived from the following question.
• Q1: What does a city want to accomplish or address?
Establishing challenging city areas and approaches to
improve them is crucial for a state-of-the-art map. With
a global acceleration towards sustainable development,
cities have many model guidelines to follow. The model
choice requires presenting beneficial improvement to the
current status quo.
• Q2: For whom will the changes be beneficial?
Sustainable development is structured on three dimen-
sions: economic, environmental and social. The city
structure is similar to sustainable development, with an
artificially created ecosystem comprising living organ-
isms (parks, waterways), inhabitants (businesses, residen-
tial areas, services) and infrastructure (buildings, public
transport). Any development, similar to sustainable devel-
opment, should promote beneficial improvements to all
actors within the city.
• Q3: What will the changes affect when implemented?
The complexity of the city system and its subsystems pre-
sents a challenge to any solution implementation and the
changes it will bring. Improvement in one subsystem (e.g.
energy production) could enhance the livelihood of inhab-
itants while decreasing the negative impacts on the envi-
ronment. Therefore a holistic approach is suggested when
evaluating solutions' effects on city.
The measure phase continues the process of the define
phase and implements several initial setups, most notably the
established value streams from the previous stages. Multiple
iterations are possible until satisfactory results are gained.
The phase needs to resolve two key factors by conducting
activities such as (1) create a measurement scope, (2) pre-
pare a wholesome measurement system, (3) validate meas-
urement systems and (4) collect statistical data.
• Q4: What data is vital to attain for accomplishing the
city’s goals?
The established value streams and plans refer to needed
data for attaining goals. The data is then transformed into a
“state-of-the-art”, referring to areas of interest, and statisti-
cal database creation as the basis for comparison after the
implementation of solutions.
• Q5: How to attain the needed data?
Several approaches can be undertaken when referring to data
type—establishing procedures to garner data and associating
tools, frameworks and technologies enabling it. Data should
be reliable, available for further analyses and computable
between different technical systems.
Statistical data gathered in the measure phase is analysed
in the analysis phase. Multiple iterations of actions such as
(1) appropriate tools and framework choice for conducting
analyses, (2) gained data statistic analysis, (3) statistical
results validation, (4) “state-of-the-art” and “hot-spot” crea-
tion and (5) issue identification and systematic distribution
by available resources might be needed, until mid-goals are
fulfilled and a follow-up with the next phase is possible.
• Q6: What is the city’s current standing?
As already considered in the measurement phase, the
most comprehensive way to establish cities current state is
through statistically available data. The analysed data pro-
vides guidelines for establishing a holistic overview of areas
and subsystems. These areas are crucial for decision-makers,
experts and researchers for area evaluation and distribution
importance of addressing.
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
51A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
• Q7: How far away from the set goals are we?
A comparison between the goals and the current state can
be established. Understanding our standing is essential, as
it provides insight into identified challenges and systematic
distribution by considering the funds, technology, policies,
and workforce needed to address them.
In the improve phase, we can follow-up on the estab-
lished initial approaches and their availability, focusing on
their implementation in practice. Solutions performance is
constantly measured until satisfactory progress in-line with
the proposed results. This is achieved through actions: (1)
potential solution development, (2) solution evaluation,
(3) solution optimisation, (4) solution compliance valida-
tion to a circular and sustainable approach and (5) solution
implementation.
• Q8: Which solutions are most appropriate, and how to
implement them?
Solution selection to address identified issues must follow
sustainable development and chosen city model core attrib-
utes. Following the selection, a holistic plan for solution
implementation is conducted, considering legal limitations,
funding, and technology availability.
• Q9: How will the implemented solutions improve current
standing?
Both questions should be considered simultaneously. The
selected solutions considered for realisation need to provide
visible improvements across all affected areas.
The control phase represents the conclusion of the entire
process. If an appropriate approach is considered, it can also
act as an initiator of semi-loops or continuous circular loops,
theoretically promoting and enabling a constant process of
improvement and progress. In hindsight, creating such a loop
can help further development towards sustainable develop-
ment and circularity or, to a degree, maintain the status quo
achieved through the whole DMAIC process. Loop crea-
tion is achieved through actions (1) indicator set creation,
(2) indicator set validation, (3) indicator implementation for
regular monitoring, (4) ensuring a maintainable improve-
ment process and (5) semi- and final-loop creation.
• Q10: What indicators to create and use for measuring
checks in the city?
After the solutions realisations, there is a clear need to estab-
lish a monitoring system for either an unspecified or speci-
fied time. The reverse information flow feeds the established
statistical database. For further improvement, a measurement
system with a compatible indicator framework is needed to
measure the new values. The acquired data, compiled with
existing data, can be processed for reports and presented
to raise public awareness and potential investors and guide
policy creation or improvement.
• Q11: Which loops to establish and nurture?
The DMAIC tool's primary purpose is continuous loop crea-
tion, providing a long-term improvement process. Consider-
ing the addressed issues, not all are valid for such a loop,
established by referring to the benefits added by each itera-
tion. A “dummy” model should be created and tested for
improvement rates and, based on the results, considered if
applicable for inclusion into a semi-loop.
Case study Maribor anddata collection
Maribor is the regional capital of the statistical region
“Podravska”, the second largest city in Slovenia. Maribor
covers 40.96 km2 (MOM 2022). According to the Statistical
Office of the Republic of Slovenia (SURS,2022), Maribor
has 96.302 inhabitants in 2022. Maribor actively follows
sustainable development guidelines, as detailed in Euro-
pean Circular Economy Action Plan (European Commis-
sion 2015), Green Deal (European Commission, 2021) and
Slovenian Development Strategy 2030 (Government of the
Republic Slovenia 2017). For this reason, it joined the con-
sortium Circular Cities and published its declaration (ICLEI
2023a) and cooperated in the "Deep demonstration" circular
Slovenia project, a joint operation by the EIT Raw Materials,
EIT Climate-KIC, the Joint Research Center of the Euro-
pean Commission, and the Government of the Republic of
Slovenia (Kovačič Lukman etal. 2022). Maribor adopted its
Circular Economy strategy in 2018 ( CORDIS,2018) and
actively monitors and reports its progress to Circular Cities
consortium (ICLEI 2023a). The reports were further used
for the basis for evaluation of current circular development
of Maribor and projects.
Results
This section represents content analysis results, establish-
ment of circular research fields and comparative analysis
with current standing of Maribor. The content analysis is
followed up by a case study analysis of Maribor based on
the DMAIC model phases.
Content analysis
We carried out a content analysis to identify current trends
in city models, with focus on circular city. The publications
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
52 K.Brglez et al.
1 3
related to the city models have indicated an irregular distri-
bution, yet a visible increase between 2019 and 2021.
From Fig.3, we can perceive that the number of publica-
tions increased significantly from the initial year, attaining
peaks in multiple years depending on the city model. The
highest number of publications in the case of the circular
city was detected in 2021, smart city in 2022 and green city
in 2019. The overall increase in publications related to city
models can be attributed to the inclusion of cities within
the UN Sustainable development goals (SDGs 17) for green
cities, the adoption of the circular economy action plan in
2015 for circular cities, while smart cities the increased
interest and growth of blockchain technology and recogni-
tion by organisations such as EU, UN. The interest in each
specific city model lies in what wants to be achieved by its
implementation. For green cities, this is incorporating green
spaces, an increased sustainable approach to food produc-
tion, and green practices in industry and society. For smart
cities, this is the implementation of digital technology and
solutions, IoT, and big data, spearheading the fourth indus-
trial revolution. Meanwhile, for circular cities, this can be
attributed to improving energy production and consump-
tion, improving waste management, increasing circulation
in loops for extended periods, and preserving resources for
future generations.
WoS enables multiple analyses capabilities surveys,
including publication distribution analyses according to sub-
ject categories. The database comprehends approximately
250 subject categories and research areas, which provide
insight into the city model evolution. The subject categories
distribution per city model can be seen in Table3.
We can perceive similarities between the distribution per
subject category, indicating a common research field for
all the city models. These fields are perceived from subject
categories. For example, such as Environmental Sciences,
Green Sustainable Science, and Environmental Studies.
Thus, environmental-related research fields are at the fore-
front of all three city models, while additional fields were
detected for separate city models. In the case of smart cities,
there is a clear focus on digital technologies, supported by
the fact of categories such as Computer Science Informa-
tion Systems (n = 61), Computer Science Theory Methods
(n = 58) and Engineering Electrical Electronic (n = 57). The
circular city focuses on energy production and consumption,
visible by categories of Engineering (n = 26) and Energy
Fuels (n = 23). A similar notion can be perceived for the
green city with its focus towards urban planning of green
spaces due to categories Regional Urban Planning (n = 12),
Urban Studies (n = 12) and Transportation (n = 6). Addi-
tional analysis within the WoS platform included the jour-
nals that identified a total of n = 455 publication titles for
all the city models. With multiple publications identified
across the model, only the top 10 journals were considered
and presented in Table4.
We can perceive a similar distribution to subject catego-
ries attributed to all the observed city models, for example,
Sustainability, Sustainable Cities and Society. As for catego-
ries, there is also some specific orientation for publications.
For smart cities, it is again focused on computer sciences,
e.g. Lecture Notes in Computer Science (n = 8) and Pro-
gress in IS (n = 8). The circular city is more oriented towards
increased circularity of resources, as visible by the Journal
of Cleaner Production (n = 11) and Resources Conservation
and Recycling (n = 3). For the green city, we can once again
discern increased interest towards environmental technology,
urban planning and human health, with publications such as
Environmental Technology Innovation (n = 2), Inter national
Journal of Environmental Research and Public Health (n = 2)
and Town Planning Review (n = 2).
Fig. 3 Number of published
papers per city model ranging
from 2012 to the 2022year
1000
43
10 8
15
21
4
1
11
45
35
26
59
41 40
56 59
63
32313
76
18
10 97
0
10
20
30
40
50
60
70
2012 2013 2014 2015 2016 20172018201920202021 2022
Publicationno.
Year
Circular City SmartCityGreenCity
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
53A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
We have employed Leximancer to model concepts to dis-
cern interactions between the employed city models. The
initial settings within the Leximancer were the collection
of 517 documents. The second phase entailed concept gen-
eration, where we merged concepts with the same semantic
meaning, e.g., economy and economies, as Engstrom etal.
(2022) suggested. The city models were constructed and
implemented as tags for distinct overviews in the final con-
cept map (Wilk etal 2021). The concept map comprised
62 unique concepts with three tags. Multiple reclustering
processes were implemented in the final phase to establish
logical themes (Engstrom etal. 2022). The final concept map
comprehends four significant themes: city, urban, systems
and circular, see Fig.4.
As perceived from the obtained concept map, the domi-
nant theme is city, comprising concepts ‘smart’, ‘technol-
ogy’, ‘services’, and ‘concept’, implying research towards
the smart city conceptual model. Other identified con-
cepts included ‘digital data’, ‘network’, ‘control’ and
‘information’, indicating development towards smart con-
trol system solutions. Another cluster consisted of concepts
‘public’, ‘knowledge’, ‘support’, and ‘solutions’ that can be
related to increase public awareness of digital technologies.
The second theme was urban, comprising concepts of
‘planning’, ‘environmental’, ‘population’, ‘development’,
and ‘planning’, indicating a systematic and sustainable
approach towards urban development. Another concept clus-
ter included ‘global’, ‘local’, ‘natural’, ‘resources’, ‘commu-
nity’, and ‘activities’, emphasising establishing and improv-
ing resource flows within urban communities.
The third identified theme was systems, consisting of
two clusters. The first cluster included concepts of ‘perfor-
mance’, ‘framework’, ‘process’, ‘management’ and ‘model’,
indicating a managerial and systematic approach towards
city development. ‘Projects’, ‘energy’, ‘implementation’,
‘design’ and ‘building’ concepts comprised the second clus-
ter, implying designing energy-efficient infrastructure on the
scale of city projects.
Table 3 Ten most frequent WoS
subject categories for smart,
circular and green cities
City model WoS subject category No. of hits
Smart city Green sustainable science technology 64
Urban Studies 63
Computer Science Information Systems 61
Computer Science Theory Methods 58
Engineering Electrical Electronic 57
Environmental Sciences 46
Environmental Studies 43
Regional Urban Planning 38
Computer Science Interdisciplinary Applications 36
Telecommunications 33
Circular city Environmental Sciences 49
Geography 27
Engineering 26
Energy Fuels 23
Business Economics 3
Architecture 2
Art 2
Meteorology Atmosphere Science 1
Materials Science 1
Biodiversity Conservation 1
Green city Green Sustainable Science Technology 24
Environmental Sciences 17
Environmental Studies 14
Regional Urban Planning 12
Urban Studies 12
Transportation 6
Engineering Environment 5
Computer Science Theory Methods 3
Economics 3
Management 3
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
54 K.Brglez et al.
1 3
The last theme was circular, which included two clusters.
Concepts ‘indicators’, ‘value’, and ‘materials’ formed a clus-
ter related to establishing measurement systems for flows
within city. ‘Economy’, ‘waste’, ‘production’, ‘activities’ and
‘water’ comprised the second cluster, which indicated imple-
menting a circular economy within city activities.
The position of city model tags provides additional per-
spective for research fields. A likelihood concept consisting
of city models was established, comparing only concepts
with the highest likelihood towards a city model. For a smart
city some concepts with the highest interaction rate were
‘smart’, ‘technology’, ‘control’, and ‘citizens’. The most
critical aspects of smart cities are implementing innovative
or digital technologies, accelerating greater control over the
flow of digital or "big" data in cities and increasing citizens'
digital knowledge, governance, services and systems. In cir-
cular city concepts, the highest interaction rate was detected
for circular materials, waste, production and economy. The
acceleration of circular economy principles and material
flows through resource circulation can be considered at the
forefront of circular cities. In the green cities case, the high-
est interaction rates were discovered for green area, land,
health, population and nature. Application of green technol-
ogy, green areas within urban areas, environment and human
population health improvement can be considered as focal
for green cities.
Content analysis also identified resemblance and diver-
sity in research areas. Considering the identified concepts
from the thematic map (see Fig.4), we have combined
them by semblance into research fields. Including the like-
lihood between the city model and concepts considered in
a research field, we were able to rate their importance as
visible in Fig.5.
Our analysis has identified twenty-seven research fields
derived from content analysis. These fields align with sus-
tainable development, built environment, and urban planning
Table 4 Ten most frequent
journals for smart, circular and
green cities
City model Journal No. of
publica-
tion
Smart city Sustainability 26
Cities 16
Sustainable Cities and Society 12
IOP Conference Series Earth and Environmental Science 8
Lecture Notes in Computer Science 8
Progress in IS 8
Applied Sciences Basel 5
smart Cities 5
Technological Forecasting and Social Change 5
Communications in Computer and Information Science 4
Circular city Sustainability 14
Journal of Cleaner Production 11
Resources Conservation and Recycling 3
Sustainable Cities and Society 3
Urban Geography 3
Blue-green Systems 2
Open House International 2
Water 2
Applied Science Basel 1
Business Strategy and the Environment 1
Green city Transportation Research Procedia 5
Strategies for Sustainability 4
Sustainability 3
Environmental Technology Innovation 2
International Journal of Environmental Research and Public Health 2
IOP Conference Series Materials Science and Engineering 2
Journal of Environmental Planning and Management 2
Town Planning Review 2
Urban Forestry & Urban greening 2
Baltic Journal of Economic Studies 1
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
55A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
as the foundational concepts shared by the three city models.
The research fields reflect cities' pursuit of sustainability,
although variations exist. Smart cities prioritise digitali-
sation, urban interconnectedness, and digital literacy. Cir-
cular cities emphasise economic aspects, material flows,
value creation, and energy production. Green cities focus on
environmental improvement, urban area redesign for green
practices, and public health enhancement. Industry inclusion
pertains to advancing green technology.
The research fields identified underscore the specialised
focus of each city model within the core conceptual frame-
work. By incorporating these core concepts, individual city
models can be enhanced and refined for effective real-world
implementation. To ensure accuracy and specificity in rela-
tion to circular cities, we conducted a comprehensive con-
tent analysis encompassing relevant publications, thereby
enabling us to discern research fields directly aligned with
circular cities and identify areas that are relatively less rep-
resented. This approach facilitates model optimisation. Our
Fig. 4 City model relation
to publication on city core
concepts
Fig. 5 The interaction among
city models and research fields
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
56 K.Brglez et al.
1 3
findings yield a concept map comprising 44 unique concepts
distributed across four distinct themes: circular economy,
waste, urban space, and sustainable development (refer to
Fig.6 for visualisation).
The most dominant theme identified was circular econ-
omy, which included concepts ‘circular city’, ‘social’, ‘sys-
tems’ and ‘environmental’, indicating relatedness towards
sustainable development dimensions. The other relevant
cluster included concepts ‘resources’, ‘flows’ and ‘manage-
ment’, indicating system development to manage resource
flows.
The second theme was waste, where two three clusters
were detected. Concepts such as ‘waste’, ‘energy’, ‘water’
and ‘food’ were identified to be related to the Water-Energy-
Food-Waste nexus. Concepts ‘materials’, ‘consumption’,
‘waste’, ‘recycling’ and ‘recovery’ are related to promoting
resource circulation. The third cluster was shared with the
circular economy.
In the theme of urban space, the concepts ‘building’ and
‘infrastructure’ refer to the built environment or inanimate
city park, while ‘public’ and ‘services’ present the live city
part and their influence on city development. The importance
of interaction between society and the built environment is
visible in the concepts ‘human’ and ‘heritage’, referring to
the cultural, and historical meaning cities have to society
and the issues of preserving them by a sustainable approach.
The theme of sustainable development exhibited the least
dominance, characterised by concepts such as ‘planning’ and
‘process’, indicating a systematic and well-planned approach
to city transformation. Additionally, the concepts of ‘human’
and ‘heritage’ suggest a focus on the preservation of cultural
heritage within cities. Building upon the initial identifica-
tion of twenty-seven research fields, we further conducted
content analysis of circular city research papers, leading to
the identification of twenty-four additional research areas
deemed essential for an optimal circular city model. These
established research areas were subsequently employed
to evaluate the city of Maribor, with variations in colour
reflecting the inclusion of individual areas within Maribor
(see Fig.7).
Maribor demonstrates active engagement in becoming a
circular city, aligning with its commitment to implementing
a circular economy strategy. Our analysis indicates substan-
tial progress in various areas, particularly concerning sus-
tainable development dimensions such as water, waste, and
resource management, as evident from current development
reports. However, certain areas warrant further attention,
including establishing smart and digital network systems,
effective construction management, education on circular
economy and circular city concepts, and efficient supply
and value chain management. Additionally, addressing
health, environmental costing, circular built environment,
and performance management within Maribor's forthcom-
ing circular strategies is essential. These areas represent
valuable opportunities for Maribor to advance its circular
initiatives and reinforce its commitment to sustainable urban
development.
Conceptual model onthecase ofMaribor
After assessing Maribor using the established research
fields, we proceeded with a case study employing our
conceptual model, based on the guideline questions and
actions needed (see Fig.2), and implemented. Publicly
accessible project documentation and declarations formed
the foundation for addressing the corresponding questions
in each phase. During the Define phase, we derived the
following conclusions based on our analysis.
Strategic approach creation andconstrains identification
Maribor demonstrates compliance with both national and
international policies, including Directive 98/2008/EC and
the Slovenian Development Strategy 2030. As part of its
circular management strategy, Maribor aims to integrate
various sectors, including municipal waste, construction,
Fig. 6 Circular city concept map
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
57A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
industry, energy, water management, land usage, and
social mobility. This holistic approach seeks to establish
a comprehensive managerial system that effectively gov-
erns all available resources within the city and its broader
urban area.
City holders, stakeholders andother public groups
inclusion
The changes aim to improve the cities and wider urban area
cooperative economy. The target group of the circular strat-
egy are public companies, inhabitants, industry and local
government. Implementing the goals will increase coopera-
tion between all stakeholders and benefit the surrounding
areas with which the city cooperates already.
Value stream creation
The successful implementation of the circular economy is
anticipated to optimise resource flows within cities, enhanc-
ing their self-reliance and reducing the consumption of
natural resources. Moreover, it is expected to bolster using
renewable energy sources, promote efficient water consump-
tion, and facilitate sustainable land management. The antici-
pated benefits encompass improved economic conditions for
all stakeholders by creating new green employment opportu-
nities, reducing environmental impact, and generating value-
added economic growth. Additionally, this endeavour aims
to foster the development of proprietary technologies and
innovative research and development models. Maribor has
laid a solid foundation for the subsequent stages in the light
of the preliminary phase.
During the measurement phase, we specifically focused
on two pivotal inquiries, the details of which are presented
below. By analysing the gathered data, we have formulated
the corresponding responses tailored to Maribor's context.
Tools, framework andmeasurement choice andvalidation
The project team swiftly recognised the necessity of estab-
lishing and maintaining a statistical database for Maribor.
The primary objective was to acquire data on specific areas
identified during the Define phase. The objective encom-
passed municipal waste, construction and demolition waste,
soil composition and health, heat and renewable energy gen-
eration and utilisation, sustainable mobility, water reuse and
recycling, land management, and regenerating degraded land
areas. The data collection process adhered to circular indi-
cators developed by CityLoops, serving as a framework for
gathering data essential for reports and analysis while also
facilitating the measurement and validation of the collected
raw data.
Fig. 7 Research areas required for optimal circular city model and evaluation of Maribor
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
58 K.Brglez et al.
1 3
Collecting statistical data
Data acquisition will be accomplished by implementing
material flow analyses (MFA) examining the urban area's
current resource flows. To obtain the necessary raw data
for MFA, individual statistical databases from companies
(e.g. Snaga d.o.o., Marprom d.o.o., Nigrad d.o.o.), as well
as regional and national statistical databases from SURS,
and locally generated statistical data by Maribor, will be col-
lected. The gathered data will be stored and analysed at Mar-
ibor's dedicated resource management centre. This centre
will serve as an observatory and knowledge hub, facilitating
the city's enhancement and dissemination of circular knowl-
edge management practices. Based on the findings of this
foundational effort, Maribor identified the areas requiring
measurement and devised a systematic approach to gather
the requisite data, thereby accomplishing all objectives of
this phase.
The analysis phase is tightly interconnected with the
measurement phase, as it is a continuation of managing the
gathered raw statistical data. The main goal here was thus
identifying what approach did Maribor city followed in ana-
lysing the gathered data, conducting following actions.
Solution development, evaluation andoptimisation
Based on research and analysis published in the relevant
literature, the project team has identified several primary
areas based on the gathered data for immediate attention.
In the context of Maribor, these areas primarily encompass
waste management improvements aimed at gradually phas-
ing out landfill waste, enhancing recovery rates, increasing
recycling rates, and promoting material reuse. A second
critical area involves optimising heat usage within the heat-
ing district centre by expanding the utilisation of renewable
resources. Regarding sustainable mobility, the focus lies on
gradually restricting road vehicle access to the city centre
while enhancing public transport options and promoting
alternative modes of transportation such as bicycles. The
water sector emphasises reducing current losses, minimising
unnecessary consumption, and increasing recovery rates by
implementing advanced filtration techniques and wastewater
recycling. The cooperative economy sector targets imple-
menting sharing economy concepts, promoting material and
product reuse, and initiating building reconstruction projects
within the city. Lastly, attention is devoted to regenerating
degraded areas impacted by industrial activities, transform-
ing them into vibrant green spaces. Based on analysis and
research, these findings contribute to the scientific com-
munity and provide a comprehensive foundation for future
endeavours in sustainable urban development.
“State oftheart”, “hot‑spot” creation andsystematic
identification anddistribution ofresources
A SWOT analysis was conducted to evaluate the current
state of Maribor. The analysis revealed that Maribor had
already implemented a Sustainable Urban Strategy and had
emerged as a prominent centre for advancing the circular
economy in Slovenia. Furthermore, a comprehensive Road-
map towards a circular economy had been established, serv-
ing as a foundation for future progress. As a result, many
goals outlined in the circular strategy for 2018 had been
either fully or partially accomplished by 2023. However,
the most pressing challenges in Maribor presently revolve
around land regeneration, reducing and recycling water
usage, establishing cooperative economy networks, and uti-
lising renewable energy sources and surplus heat. Despite
these challenges, Maribor demonstrated a well-structured
approach to data analysis, facilitating identifying potential
solutions for the existing circumstances.
The improve phase relied heavily on the results of anal-
ysis phase, as it enabled an insight into current state and
identification of potential areas for improvement. This are
achieved through analysis of activities by Maribor related to
needed actions to achieve them.
Solution development, evaluation, optimisation
andimplementation incompliance withcircular
andsustainable approach
For the phase, we have analysed projects, either active or
finalised, where Maribor city addressed the areas deemed
challenging to accelerate the city's transformation towards
a circular one. Improvement for waste management, con-
sidered solution related to transforming waste management
activities to comply with the circular economy approach,
developing own comprehensive business system for man-
aging material flows within theMunicipality of Maribor
(MOM) and increasing recycling rates by closing loops for
resource leakage. The social aspects considered establish-
ing a monitoring network for prolonging product usage in
the loop (reuse, refurbishment, repair ships) and educating,
raising awareness and increasing integration of all stakehold-
ers (citizens, organisations, administration). Nigrad Maribor
partially achieved set goals for the area by joining the project
"CINDERELA" within the Horizon 2020 CIRC: 2016–2017
grant framework (CORDIS 2018). The project's main goal
entailed improving construction and demolition waste, as
it represents the largest collected share within urban areas.
The project encourages using secondary raw materials from
recycled construction and industrial waste. The aimed results
is creating a circular resource utilisation model that could
reduce negative environmental impacts by up to 20% and
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
59A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
increase the recycling rate of waste from the construction
sector by up to 30% (CINDERELA 2023).
The optimisation of energy utilisation for heat and
electricity production and the incorporation of renewable
resources are key strategies being implemented in Mari-
bor to address current heat usage and increase the utilisa-
tion of renewable energy sources. These efforts involve the
construction of heat storage facilities, utilising landfill gas,
biogas, and synthesis gas derived from biological waste, and
efficiently utilising available surplus heat. In collaboration
with the circular economy-HEAT consortium, the Maribor
Waste Management Centre has successfully implemented
a project that utilises waste heat from electricity production
to heat a museum (circular economy HEAT 2019). Addi-
tionally, Energetika Maribor, in partnership with MOM,
is currently engaged in a project focused on incorporating
thermal energy solutions. The project aims to achieve 60%
energy self-sufficiency by expanding the hot water net-
work and connecting facilities in densely populated areas
by 2020 (ManagEnergy 2022). The goals include integrat-
ing renewable energy sources such as solar and biowaste to
reduce CO2 emissions, ensure the affordability of energy
and heat, and distribute them efficiently to the local popu-
lation. Furthermore, MOM has completed a collaboration
with ENERGAP in a project titled "Energy refurbishment of
twenty-four public buildings in the City of Maribor using the
Energy Contracting model", which aims to improve energy
efficiency and increase self-sufficiency through the use of
renewable energy sources (FEDARENE 2021). This project
is estimated to reduce energy consumption by 5,952 MWh,
costs, and CO2 emissions.
Maribor has undertaken various projects to promote sus-
tainable transportation, with some still in progress and oth-
ers completed. A current initiative led by Maribor is the
"MBAJK" project, which focuses on the sharing economy
and the promotion of sustainable and healthy transport. This
project, scheduled to run until 2037 (MOM 2023a), aims to
establish a public bicycle rental/sharing system within the
Maribor Waste Management Centre (MOM). The system
is already operational and improved with IT assistance and
adding more bicycle charging stations. Additionally, Mari-
bor has made improvements to logistical infrastructure to
facilitate business development (MOM 2023b, 2023c) and
enhance public spaces for recreation (MOM 2023d; 2023e),
with these enhancements completed in 2022. The decision
to restrict traffic in the city centre has increased the impor-
tance of effective logistical planning. In response, Mari-
bor is developing a project to establish an enclosed market
where residents can sell meat and dairy products, reducing
the reliance on regional supply chains (MOM 2023f). These
projects in Maribor collectively contribute to the advance-
ment of sustainable transportation, the promotion of shar-
ing economy principles, the improvement of logistical infra-
structure, and the enhancement of public spaces.
Maribor, as a partner city, collaborated on "The City
Water Circles" (CWC) project under the umbrella of the
"Interreg" organisation. Within this collaboration, a pilot
project called "Secondary Raw Material from Rain and
Wastewater in Maribor" was undertaken and concluded in
2022 (Interreg Europe 2022). The pilot project focused on
water recycling and alternative water resource usage. One
of the main objectives was to reintroduce purified wastewa-
ter and rainwater into the construction sector as secondary
raw materials. A storage and collection unit for rainwater
was established, and purified wastewater from local treat-
ment plants was transported for reuse. The obtained mate-
rials were utilised for road maintenance and revitalising
degraded areas, specifically targeting the degraded urban
area in Dogoše. The project's outcomes demonstrated that,
despite higher initial costs compared to conventional water
usage, the incorporation of purified wastewater and rainwa-
ter reduced average costs by 25% when considering envi-
ronmental impacts and associated costs (Interreg 2023). The
project highlights the potential economic and environmental
benefits of utilising alternative water resources in construc-
tion activities.
In collaboration with the University of Maribor, Mari-
bor is actively engaged in the European Union Regenerative
Urban Lighthouse (UPSURGE) project. This initiative aims
to develop city models centred on Nature-Based Solutions
(NBS) and address urban area degradation and revitalisa-
tion. As part of UPSURGE, Maribor is undertaking a pilot
study focused on the waterway of the Pekrski River. The
pilot study aims to establish a green corridor, implement
pocket gardens, and introduce blue infrastructure along the
Pekrski River. These measures are intended to enhance the
ecological quality and livability of the area. The project is
yet to be implemented (UPSURGE 2023). By incorporat-
ing Nature-Based Solutions and promoting sustainable urban
development, the city aims to achieve its circular economy
goals.
The control phase represents a conclusion to the estab-
lished model and the phase that starts a continuous improve-
ment process, initiating another round of the whole DMAIN
circle. Five actions need addressing in this phase.
Indicator set creation, validation
The analysed projects in this study have established spe-
cific indicators for measurement and analysis purposes.
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
60 K.Brglez et al.
1 3
These indicators enable continuous monitoring and provide
opportunities for improvement. Maribor's circular economy
strategy aligns with the circular city indicators developed
by ICLEI (2023b). By incorporating these indicators and
implementing measurement systems during the analysis
phases, Maribor has adopted a systematic approach to mon-
itoring its progress in transitioning towards a circular city.
This approach ensures a comprehensive evaluation of the
city's efforts and promotes the achievement of circularity
objectives.
Indicator set implementation formonitoring, maintaining
improvement process andcreation ofloops
Given the ongoing development of new projects in Maribor,
it is challenging to determine the specific loops to estab-
lish at this stage. Moreover, certain projects require further
measurement and evaluation to identify potential benefits
and areas for improvement, which can inform the establish-
ment of appropriate loops. Therefore, it is recommended to
implement semi-loops involving analysis, improvement, and
control phases until all project goals are attained. Follow-
ing the initial project phase, a comprehensive assessment
of Maribor's current state is advised to facilitate the crea-
tion of an updated circular economy strategy. This approach
ensures a more informed and targeted implementation of
effective loops, enabling the city to progress towards its cir-
cular economy objectives.
Discussion
The research provided information and cooperation on devel-
oping and designing smart, circular, and green city models
from research paper content analysis. Results revealed an
increased publication number for city models. An increase
coincided for models with the introduction of SDG17 goals
by the UnitedNations (General Assembly UN2015), the
Circular Economy Action Plan for circular cities (European
Commission 2015; European Commission 2019), and the
smart City Expo World Congress in Barcelona for smart
cities (European Commission 2019). According to the city
model orientation, differences between models were identi-
fied in publications and WoS categories.
The findings derived from the content analysis have
revealed distinct research trends concerning the conceptual
core of each city model. Smart cities, for instance, prioritise
the development of innovative technologies and services that
facilitate enhanced control over city activities and their ease
of use by residents (Moradi 2020). Additionally, there is a
growing interest in establishing smart networks and digital
databases to enable seamless communication between tech-
nology and users, with the ultimate aim of reducing environ-
mental impacts and integrating different sectors of the city
into a unified system (Tiwari etal. 2021; Hajek etal. 2022).
Consequently, implementing sustainable development in
smart cities entails the establishment of smart environments,
IoT solutions, and networks (Moradi 2020).
The analysis of green cities has revealed a distinct focus
on integrating a green mindset and technologies. The
research indicates that green cities need help attempting to
incorporate green urban planning, particularly concerning
the inclusion of green spaces and the promotion of natural
environment regeneration, which can be hindered by exist-
ing city layouts (Jia etal. 2021). However, researchers are
addressing these issues by investigating the potential benefits
and advantages of promoting a healthy, sustainable lifestyle
for residents, such as increased biodiversity and economic
opportunities (Jai etal. 2021; Zhang etal. 2022; Javidroozi
etal. 2023).
Through a cross-analysis of the three city models, a total
of twenty-seven research fields were identified. While some
overlap between the models, the results surprisingly dem-
onstrated a high degree of interaction. The overlap indicates
that city models are actively evolving and seeking potential
opportunities that can accelerate their transition towards
sustainable development. Comparisons with the findings of
Javidroozi etal. (2023) and Ahvenniemi etal. (2017) sug-
gest that cities progressively integrate proven and benefi-
cial solutions from competing city models. By adopting this
approach, cities can expedite the development of solutions,
offer established ideas to policymakers, and ultimately gain
an advantage in achieving their sustainable goals (Javidroozi
etal. 2023). The high level of interaction between the city
models indicates a positive trend towards adopting success-
ful strategies and solutions from different models, accelerat-
ing the progress towards sustainable development.
The content analysis results pertaining to circular cities
are centred around the core concept of the circular economy.
The circular cities' focus is to achieve sustainable develop-
ment in line with the goals set by the United Nations for
establishing sustainable cities (United Nations 2022). The
findings reveal key areas requiring attention to implement
circular economy principles. One important aspect is the
establishment of urban flow maps and the principles of urban
metabolism for future urban planning (Lucertini and Musco
2022). These approaches can progressively increase resource
circularity and self-sufficiency within cities (Kalmyk-
ova and Rosado 2015; Mazzarella and Amenta 2022).
Another significant area identified is the integration of the
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
61A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
Water-Energy-Food nexus with the 9R strategies. Cities are
major consumers of resources (Mulier etal. 2022), which
are often quickly disposed of. The challenge lies in retaining
these resources, and while recycling and reuse activities are
being implemented, the need for upper 9R strategies sug-
gests slow development in this regard. Research by Potting
etal. (2017) indicates that the full realisation of a circular
economy requires implementing upper strategies, which are
currently underrepresented in the literature.
Furthermore, circular cities face the challenge of improv-
ing their inhabitants' economic and social aspects while
mitigating potential environmental impacts associated with
urban development (General Assembly UN 2015; Circular
City Funding Guide 2023; United Nations 2022). Since
cities are built environments, most changes occur in infra-
structure and its utilisation for commerce, residential sec-
tors, transportation, and services. Limiting resource losses
through construction and demolition activities is crucial by
employing upper 9R strategies such as repurposing and reus-
ing existing buildings (Cimen 2021). These solutions aim
to adapt buildings to meet the proposals of the inhabitants,
thereby increasing the cultural and economic value for a
more socially sustainable urban lifestyle (Cimen 2021; EMF
2023).
The case study conducted on Maribor revealed that the
city has a well-established circular strategy. Furthermore,
by integrating this model with the research focus areas
of circular cities, a systematic analysis of the city's pro-
gress towards achieving circular goals was facilitated. The
results indicate that Maribor is aligning its activities with
its projected plans while considering all three dimensions
of sustainability as defined by the United Nations (United
Nations 2022) and the Circular City Funding Guide (2023).
However, it is important to note that the final phase of the
circular strategy, namely the control phase, has yet to be
fully established. This phase could be crucial in advancing
future planning efforts to improve circularity. The challenge
of monitoring progress is not unique to circular cities but is
also a concern for smart cities (Lai and Cole 2023) and indi-
vidual sectors (Zope etal. 2019; Batalhao and Texeira 2020).
As the authors point out, the main issue lies in establishing
effective monitoring management systems that assess the
current situation and provide data for future development.
The results gained from our case study and content
analysis, suggest that cities are implementing project
oriented approach in establishing circular activities
in cities. The main issue is not implementing circular
approach, but establishing monitoring management, that
would enable assessing current standings, benefits and
provide groundwork for future strategies and policies to
be employed (Marin etal. 2020; Henrysson etal. 2022).
Future projects should provide monitoring frameworks
with circular city indicators (Vangelsten etal. 2020; Lind-
green etal. 2020; Paoli etal. 2022), establishing a con-
sequential “state-of-the-art” map of the progress towards
circularity. Continuous improvement and promotion of
more permanent loops are dependable on the progress we
achieved and needed to attain sustainable development,
as our established city model constituted in the control
phase.
Conclusion
Gaining insights into current research trends and the core
conceptual evolution of city models is crucial for achiev-
ing sustainable development. While each city model
pursues its approach to sustainability, their specialisa-
tion presents an opportunity for improvement through
cross-pollination. The content analysis identified simi-
larities and differences among the smart, circular, and
green city models and twenty-seven research trends that
correspond to all three city models. Such identification
is necessary to properly manage cites according to the
identified models.
An additional content analysis focused on circular
cities only enabled the identification of specific trends
within the circular city model. Combining the findings
with the previously established twenty-seven research
trends led to identifying twenty-four fields contributing
to the development of an optimal circular city model. To
structure these fields, we incorporated them into a con-
ceptual model based on the DMAIC framework and prob-
lem-solving tools. The results showed that DMAIC-based
tool allows cities to establish a continuous improvement
cycle in their transition towards circularity. The model
emphasises the establishment of semi-loops and loops
and, when combined with a problem-solving systematic
approach, provides a systematic and constructive means
for potential policymakers to develop circular strategy
maps.
The case study on the city of Maribor validated the
proposed model, and also revealed the current weakness
of inadequate monitoring of the progress towards a cir-
cular economy. Additional case studies focusing on the
conceptual model are necessary to validate further and
improve its application. Future research will enhance the
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
62 K.Brglez et al.
1 3
conceptualised model, particularly by establishing meas-
urement frameworks and indicators for validation dur-
ing the control phase. Understanding the effectiveness of
implemented circular activities is vital for future develop-
ment and avoiding the unnecessary expenditure of time,
funds, and resources in achieving a sustainable society.
Appendix
See Figs.8, 9, and 10.
Acknowledgements Kristijan Brglez was supported by the Slove-
nian Research Agency (Grant No. 1662/FNM-2021). Rebeka Kovačič
Lukman and Matjaž Perc were supported by the Slovenian Research
Agency (Grant No. P1-0403).
Author contribution Kristijan Brglez contributed to conceptualisa-
tion, methodology, leximancer, analysis, writing—original draft,
visualisation, resources. Matjaž Perc contributed to leximancer net-
work perspective, writing—review and editing. Rebeka Kovačič
Lukman contributed to analyses, resources (literature review), writ-
ing—original draft, visualisation, supervision, writing—review and
editing.
Funding The authors have not disclosed any funding
Data availability Enquiries about data availability should be directed
to the authors.
Declarations
Competing interests The authors declare that they have no known
competing financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
were made. The images or other third party material in this article are
included in the article's Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not included in
the article's Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.
Fig. 8 Major themes relatedness to smart city model
Fig. 9 Major themes relatedness to circular city model
Fig. 10 Major themes relatedness to green city model
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
63A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
References
Ahvenniemi H, Huovila A, Pinto-Seppä I, Airaksinen M (2017) What
are the differences between sustainable and smart cities? Cities
60(5):234–245. https:// doi. org/ 10. 1016/j. cities. 2016. 09. 009
Angus D, Rintel S, Wiles J (2013) Making sense of big text: a visual-
first approach for analysis text data using Leximancer and Dis-
cursis. Int J Soc Res Methodol 16(3):261–267
Batalhão ACS, Teixeira D (2020) Chapter18—Cities management and
sustainable development: monitoring and assessment approach.
In: Verma P, Singh P, Singh R, Raghubanshi AS (eds) Urban
ecology. Elsevier, Amsterdam, pp 335–354
Biesenthal C, Wilden R (2014) Multi-level project governance: trends
and opportunities. Int J Proj Manag 32(8):1291–1308
Biesialska K, Franch X, Muntes-Mulero V (2018) Protocol and tools
for conducting agile software engineering research in an indus-
trial-academic setting: a preliminary study. In: Circular econo-
mySI´18: proceedings of the 6th international workshop on con-
ducting empirical studies in industry, pp 29–32. https:// doi. org/
10. 1145/ 31939 65. 31939 70
Birgovan AL, Lakatos ES, Szilafyi A, Cioca LI, Pacurariu RL, Ciobanu
G, Rada EC (2022) How should we measure? A review of cir-
cular cities indicators. Int J Environ Res Public Health 19:5177
Biroscak BJ, Scott JE, Lindenberger JH, Bryant CA (2017) Leximancer
software as a research tool for social marketers: application to a
content analysis. Soc Mark Q 23(3):223–231
Blomsma F, Brennan G (2017) The emergence of circular economy:
a new framing around prolonging resource productivity. J Ind
Ecol 21(3):603–614
Boeri A, Gaspari J, Gianfrate V, Longo D, Boulanger SOM (2019)
Circular city: a methodological approach for sustainable dis-
tricts and communities. WIT Trans Built Environ. https:// doi.
org/ 10. 2495/ ARC18 0071
Bornmann L, Leydesdorff L (2014) Scientometrics in a changing
research landscape: bibliometrics has become an integral part
of research quality evaluation and has been changing the prac-
tice of research. EMBO Rep 15(12):1228–1232
Campbell C, Pitt LF, Parent M, Berthon PR (2011) Understand-
ing consumer conversations around ads in a web 2.0 world. J
Advert 40(1):87–102
Cerreta M, di Girasole EG, Poli G, Regalbuto S (2020) Operational-
izing the circular City Model for Naples’City-Port: a Hybrid
Development Strategy. Sustainability 12:2927
Chakravorty S, Hales DN, Herber JI (2008) How problem-solving
really works. Int J Data Anal Tech 1(1):44–59
Çimen Ö (2021) Construction and built environment in circular
economy: a comprehensive literature review. J Clean Prod
305:127180
CINDERELA (2023) Blueprint for a resource-efficient secondary
raw material based urban and periurban construction sector.
CINDERELA. https:// www. cinde rela. eu/ The- proje ct/ Repor ts/
D3.4- Bluep rint- for-a- resou rce- effic ient- secon dary- raw- mater
ial- based- urban- and- periu rban- const ructi on- sector. Accessed
14 January 2023
Circular City Funding Guide (2023) Built environment. Circular City
Funding Guide. https:// www. circu larci tyfun dingg uide. eu/ circu
lar- sector/ built- envir onment/. Accessed 14 Jan 2023
Circular economy HEAT (2019) Comprehensive model of waste
heat utilization in circular economy regions. Interreg Central
Europe. https:// www. ezavod. si/ en/ eu- proje cts/ ongoi ng- proje
cts/ low- carbon- socie ty/ ce- heat# proje ct- infor mation. Accessed
12 Jan 2023
CORDIS (2018) New circular economy business model for more
sustainable urban construction. European Commission. https://
cordis. europa. eu/ proje ct/ id/ 776751. Accessed 12 Jan 2023
Cretchley J, Rooney D, Gallois C (2010) Mapping a forty-year history
with Leximancer: themes and concepts in circular cities. J Cross
Cult Psychol 4(3):318–328
Crippa J, Silva MG, Ribeiro ND, Ruschel R (2022) Urban branding and
circular economy: a bibliometric analysis. Environ Dev Sustain
24(6)
De Mast J, Lokkerbol J (2012) An analysis of the Six Sigma DMAIC
method from the perspective of problem solving. Int J Prod Econ
139(2):604–614. https:// doi. org/ 10. 1016/j. ijpe. 2012. 05. 035
Dodman D, Diep L, Colebrander S (2017) Resilience and resource
efficiency in cities. UNEP, New York
EMF (2023) First steps towards a circular built environment. Ellen
MacArthur Foundation. https:// ellen macar thurf ounda tion.
org/ artic les/ first- steps- towar ds-a- circu lar- built- envir onment.
Accessed 14 Jan 2023
Engstrom T, Strong J, Sullivan C, Pole JD (2022) A Comparison of
Leximancer semi-automated content analysis to manual content
analysis: a healthcare exemplar using emotive Transcripts of
COVID-19 Hospital staff interactive webcasts. Int J Qual Meth-
ods 21:1–13
European Commission (2015) First circular economy action plan.
European Union. https:// ec. europa. eu/ envir onment/ circu lar-
econo my/ first_ circu lar_ econo my_ action_ plan. html. Accessed
12 Jan 2023
European Commission (2021) Delivering the European green Deal.
European Union. https:// commi ssion. europa. eu/ strat egy- and- pol-
icy/ prior ities- 2019- 2024/ europ ean- green- deal/ deliv ering- europ
ean- green- deal_ en# docum ents. Accessed 12 Jan 2023
European Comission (2022) Circular cities and regions initiative. Pub-
lications Office of the European Union, Luxembourg
European Union (2019) Strategy for the transition to circular economy
in the municipality of maribor. European Union. https:// circu
larec onomy. europa. eu/ platf orm/ en/ strat egies/ strat egy- trans ition-
circu lar- econo my- munic ipali ty- marib or. Accessed 4 June 2023
FEDARENE (2021) Maribor improves Energy Efficiency through Pub-
lic Buildings Refurbishment. FEDARENE. https:// fedar ene. org/
best- pract ice/ marib or- impro ves- energy- effic iency- throu gh- pub-
lic- build ings- refur bishm ent/. Accessed 12 Jan 2023
Gao J, O’Neill BC (2020) Mapping global urban land for the 21st
century with data-driven simulations and Shared Socioeconomic
Pathways. Nat Commun 11:2302
General Assembly UN (2015) Transforming our world: the 2030
Agenda for sustainable development. United Nations. https://
sdgs. un. org/ 2030a genda. Accessed 31 April 2022
Girard LF, Nocca F (2019) Moving towards the circular economy/city
model: which tools for operationalizing this model? Sustainabil-
ity 11(22):6253
Golubiewski N (2012) Is there a metabolism of an urban ecosystem?
An ecological critique. Ambio 41(7):751–764
Government of the Republic Slovenia (2017) Slovenian development
strategy 2030. Government Office for Development and Euro-
pean Cohesion Policy, Ljubljana
Gravagnuolo A, Angrisano M, Girard LF (2019) Circular economy
strategies in eight historic port cities: criteria and indicators
towards a circular city assessment framework. Sustainability
11(13):3512
Hajek P, Youssef A, Hajkova V (2022) Recent developments in smart
city assessment: a bibliometric and content analysis-based litera-
ture review. Cities 126:103709
Henrysson M, Papageorgiou A, Björklund A, Vanhuyse F, Sinha R
(2022) Monitoring progress towards a circular economy in urban
areas: an application of the European Union circular economy
monitoring framework in Umeå municipality. Sustain Cities Soc
87:104245
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
64 K.Brglez et al.
1 3
ICLEI (2023a) Circular Cities Declaration Report 2022. Local govern-
ments for sustainability. https:// circu lars. iclei. org/ resou rce/ circu
lar- cities- decla ration- report- 2022/. Accessed 4 June 2023a
ICLEI (2023b) Circular City Actions Frameworks. ICLEI. https:// circu
lars. iclei. org/ action- frame work/. Accessed 4 June 2023
Interreg (2023) CWC Online Handbook. Interreg Central Europe.
https:// progr amme2 014- 20. inter reg- centr al. eu/ Conte nt. Node/
37. html. Accessed 13 Jan 2023
Interreg Europe (2022) Fostering circular economy citizen engagement
in Maribor. Interreg Europe. https:// www. inter regeu rope. eu/ find-
policy- solut ions/ expert- suppo rt- repor ts/ foste ring- circu lar- econo
my- citiz en- engag ement- in- marib or. Accessed 4 June 2023
Jamil N, Gholami H, Mat Saman MZ, Streimikiene D, Sharif S, Zakuan
N (2020) DMAIC-based approach to sustainable value stream
mapping: towards a sustainable manufacturing system. Econ Res
33(1):331–360
Javidroozi V, Carter C, Grace M, Shah H (2023) Smart, sustainable,
green cities: a state-of-the-art review. Sust 15(6):5353. https://
doi. org/ 10. 3390/ su150 65353
Jia B, Chen Y, Wu J (2021) Bibliometric analysis and research trend
forecast of healthy urban planning for 40 years (1981–2020). Int
J Environ Res Public Health 18(18):9444
Johnson J (2012) Cities: systems of systems of systems. In: Portugali J,
Meyer H, Stolk E, Tan (eds) Complexity theories of cities have
come of age. Springer, Berlin
Kalmykova Y, Rosado L (2015) Urban metabolism as framework for
circular economy design for cities. In: Proceedings of the World
Resources Forum 2015
Kara S, Hauschild M, Sutherland J, McAloone T (2022) Closed-loop
systems to circular economy: a pathway to environmental sus-
tainability? CIRP Ann 71(2):505–528
Kovačič Lukman R, Brglez K, Krajnc D (2022) A conceptual model
for measuring a circular economy of seaports: a case study on
Antwerp and Koper ports. Sustainability 14(6):1–18
Lai CMT, Cole A (2023) Measuring progress of smart cities: indexing
the smart city indices. Urban Gov 3:45–57. https:// doi. org/ 10.
1016/j. ugj. 2022. 11. 004
Lindgreen ER, Salomone R, Reyes T (2020) A Critical review of aca-
demic approaches, methods and tools to assess circular economy
at the micro level. Sustainability 12(12):4973. https:// doi. org/ 10.
3390/ su121 24973
Long J (2020) 4 lessons from nature to build a circular economy. World
Economic Forum. https:// www. wefor um. org/ agenda/ 2020/ 11/4-
lesso ns- from- nature- to- build-a- circu lar- econo my/. Accessed 18
April 2020
Lucertini G, Musco F (2022) Circular City: Urban and territorial per-
spectives. In: Amenta L, Russo M, van Timmeren A, Regenera-
tive territories—dimensions of circularity for healthy metabo-
lisms, Springer, Cham
ManagEnergy (2022) Production and distribution of thermal energy in
the municipality of maribor. ManagEnergy. https:// www. manag
energy. eu/ node/ 1450. Accessed 12 Jan 2023
Marin J, Alaerts L, Van Acker K (2020) A Materials Bank for circular
Leuven: how to monitor ‘Messy’ circular City transition projects.
Sustainability 12(24):10351
Mazzarella C, Amenta L (2022) The circular Metabolic Urban Land-
scape. In: Amenta L, Russo M, van Timmeren A, Regenerative
territories—dimensions of circularity for healthy metabolisms,
Springer, Cham
Mingers J, Brocklesby J (1997) Multimethodology: towards a frame-
work for mixing methodologies. Omega 25(5):489–509
MOM (2022) My City. Mestna Občina Maribor. https:// marib or. si/
moje- mesto/. Accessed 4 June 2023
MOM (2023a) Establishing a system of renting/sharing public bicycles
in the Municipality of Maribor—Mbajk. Mestna Občina Maribor.
https:// marib or. si/ proje kti/ vzpos tavit ev- siste ma- izpos oje- soupo
rabe- javnih- koles-v- mestni- obcini- marib or- mbajk/#. Accessed
13 Jan 2023a
MOM (2023b) Construction of the extension of the Road of Proletar-
ian Brigades. Mestna Občina Maribor. https:// marib or. si/ proje
kti/ izgra dnja- podal jska- ceste- prole tarsk ih- briga d/#. Accessed
13 Jan 2023b
MOM (2023c) Road in the Pobrežje Zone (EPC extension). Mestna
Občina Maribor. https:// marib or. si/ proje kti/ cesta-v- coni- pobre
zje- razsi ritev- epc/. Accessed 13 Jan 2023b
MOM (2023d) Arrangement of cycling infrastructure along Zrko-
vska and Čufarjeva cesta (from the two-story bridge to Veljka
Vlahoviča Street). Mestna Občina Maribor. https:// marib or. si/
proje kti/ uredi tev- koles arsk e- infr a struk ture- ob- zrkov ski- in- cufar
jevi- cesti- od- dvoet aznega- mosta- do- ulice- veljka- vlaho vica/#.
Accessed 13 Jan 2023c
MOM (2023e) Renovation of the promenade in the City Park. Mestna
Občina Maribor. https:// marib or. si/ proje kti/ obnova- prome nade-
v- mestn em- parku/#. Accessed 13 Jan 2023d
MOM (2023f) Implementation of the meat and dairy pavilion. Mestna
Občina Maribor. https:// marib or. si/ proje kti/ izved ba- mesno-
mlecn ega- pavil jona/#. Accessed 13 Jan 2023
Monday LM (2022) Define, measure, analyze, improve, control
(DMAIC) methodology as a roadmap in quality improvement.
Lob J Qual Saf Health 5:44–46
Moradi S (2020) The scientometrics of literature on smart cities.
Library Hi Tech 38(2):385–398
Mulier MCGH, van de Ven FHM, Kirschen P (2022) Circularity in
the Urban Water-Energy-Nutrients-Food nexus. Energy Nexus
7: 100081. https:// doi. org/ 10. 1016/j. nexus. 2022. 100081
Murray A, Skene K, Haynes K (2017) The circular economy: an
interdisciplinary exploration of the concept and application in a
global context. J Bus Ethics 140(3):369–380
Sustainability N (2021) Too much and not enough. Nat Sustain
4(8):659. https:// doi. org/ 10. 1038/ s41893- 021- 00766-8
Ness D, Xing K (2017) Toward a resource-efficient built environment:
a literature review and conceptual model. J Ind Ecol. https:// doi.
org/ 10. 1111/ jiec. 12586
OECD (2021) Towards a more resource-efficient and circular economy,
OECD, Paris
Padilla-Rivera A, Russo-Garrido S, Merveille N (2020) Addressing
the social aspects of a circular economy: a systematic literature
review. Sustainability 12(19):7912
Paiho S, Wessberg N, Pippuri-Makelainen J, Maki E, Sokka L, Parvi-
ainen T, Nikinmaa M, Siikavirta H, Paavola M, Antikainen M,
Heikkila J, Hajduk P, Laurikko J (2021) Creating a circular City:
an analysis of potential transportation, energy and food solutions
in a case district. Sustain Cities Soc 64:102529
Paoli F, Pirlone F, Spadaro I (2022) Indicators for the circular City: a
review and a proposal. Sustainability 14(19):11848
Pasko O, Chen F, Oriekhova A, Brychko A, Shalyhina I (2021) Map-
ping the literature on sustainability reporting: a bibliometric
analysis grounded in scopus and web of science core collection.
Eur J Sustain Dev. https:// doi. org/ 10. 14207/ ejsd. 2021. v10n1 p303
Prendeville S, Cherim E, Bocken N (2018) Circular cities: mapping six
cities in transition. Environ Innov Soc 26:171–194
Pyzdek T, Keller P (2010) SIGMA HANDBOOK : a complete guide
for green belts, black belts, and managers at all levels, 3rd edn.
McGraw Hill Education, New York
Qayyum S, Ullah F, Al-Turjman F, Mojtahedi M (2021) Managing
smart cities through six sigma DMADICV method: a review-
based conceptual framework. Sustain Cities Soc 72:103022
Reid RA, Koljonen EL, Buell JB (1999) The deming cycle provides
a framework for managing environmental responsible process
improvements. Qual Eng 12(2):199–209. https:// doi. org/ 10. 1080/
08982 11990 89625 77
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
65A conceptual model foracircular city: acase study ofMaribor, Slovenia
1 3
Rios FC, Panic S, Grau D, Khanna V, Zapitelli J, Bilec M (2022)
Exploring circular economies in the built environment from a
complex systems perspective: a systematic review and conceptual
model at the city scale. Sustain Cities Soc 80:103411
Rosenhead J, Mingers J (2001) Rational analysis for a problematic
world revisited. Wiley, Chichester
Rosenhead J, Mingers J (2004) Problem structuring methods in action.
Eur J Oper Res. https:// doi. org/ 10. 1016/ S0377- 2217(03) 00056-0
Smith AE (2003) Automatic extraction of semantic networks from text
using Leximancer. In: Companion volume of the proceedings of
HLT-NAACL 2003—Demonstrations, pp 23–24
Smith AE, Humphreys MS (2006) Evaluation of unsupervised semantic
mapping of natural language with Leximancer concept mapping.
Behav Res Methods 38:262–279
Sokovic M, Pavletic D, Kern P (2010) Quality improvement method-
ologies—PDCA Cycle, RADAR matrix, DMAIC and DFSS. J
Achiev Mater Manuf 43(1):476–483
Sony M, Anthony J, Park S, Mutingi M (2020) Key Criticisms of six
sigma: a systematic literature review. IEEE Trans Eng Manag
67(3):950–962
Stefanakis AI, Calheiros Csmart cities, Nikolaou I (2021) Nature-based
solutions as a tool in the new circular economic model for cli-
mate change adaptation. Circular Economy and Sustainability
1:303–318
SURS (2022) Municipality maribor. Republic of Slovenia Statisti-
cal Office. https:// www. stat. si/ obcine/ en/ Munic ip/ Index/ 94.
Accessed 4 June 2023
Tiwari P, Ilavarasan PV, Punia S (2021) Content analysis of literature
on big data in smart cities. Benchmarking: Int J 28(5):1837–1857
Ulgiati S, Zucaro A (2019) Challenges in Urban metabolism: sustain-
ability and well-being in cities. Front Sustain Cities https:// doi.
org/ 10. 3389/ frsc. 2019. 00001
United Nations (2013) Sustainable development scenarios for Rio+20:
a component of the SD21 project. United Nations. https:// sdgs.
un. org/ publi catio ns/ susta inable- devel opment- scena rios- rio20-
compo nent- sd21- proje ct- 17614. Accessed 15 Jan 2023
United Nations (2019) World urbanization prospects: the 2018 revi-
sion, UN, New York
United Nations (2022) Envisaging the Future of Cities: World Cities
Report 2022. https:// unhab itat. org/ sites/ defau lt/ files/ 2022/ 06/
wcr_ 2022. pdf. Accessed 31 Aprl 2023
University of Surrey (2022) Software Review: Leximancer. Computer
Assisted Qualitative Data Analysis networking project. https://
www. surrey. ac. uk/ sites/ defau lt/ files/ 2020- 12/ cnp- lexim ancer-5-
review. pdf. Accessed 31 April 2022
UPSURGE (2023) Maribor—Slovenia. UPSURGE—Demo cases.
https:// www. upsur ge- proje ct. eu/ demo- cases/ marib or- slove nia/.
Accessed 13 Jan 2023
Urban Agenda for the EU (2023) EU multi-level governance in action.
European Union. https:// www. urban agenda. urban- initi ative. eu/.
Accessed 12 Jan 2023
Vangelsten BV, Lindeløv B, Nguyen N, Hans J Ø, Jensen A, Jacobi N ,
Clement S, Bellstedt C, Athanassiadis A, Kernel PK, Keijsers E
(2020) circular City Indicator Set. CityLoops. https:// ec. europa.
eu/ resea rch/ parti cipan ts/ docum ents/ downl oadPu blic/ ZWg0T
isyKz ZPa3h XbGxE YzNaO DNwWX lVanp qQjhD MHNkb
mxZNj lhRy8 2Y3Zp d0lzW TlBWU dRPT0=/ attac hment/ VFEyQ
TQ4M3 ptUWZ YT2kr Uk5XQ 3RyL2 FEZ3V ncTRm QTU=.
Accessed 14 Jan 2023
Wahlström M, Pohjalainen E, Teittinen T, Van der Linden A, Chris-
tis M, Mashoven S (2019) ETC report: are we losing resources
when managing Europe’s waste? European Environment Agency.
https:// www. eionet. europa. eu/ e tcs/ e tc- wmg e/ pr odu cts/ e tc- wmg e-
repor ts/ are- we- losing- resou rces- when- manag ing- europ es- waste-
1. Accessed 12 Jan 2023
Wijkman, A (2019) Circular economy in cities requires a systems
approach. Background paper for an OECD/EC workshop on 5
July 2019 within the workshop series “Managing environmental
and energy transitions for regios and cities”. OECD Publishing,
Paris
Wilk V, Cripps A, Micu A, Micu AE (2021) The state of #digitalen-
trepreneurship: a big data Leximancer analysis of social media
activity. Int Entrepreneurship Manag J 17:1899–1916
William J (2019) Circular cities. Urban Stud 56(13):2746–2762.
https:// doi. org/ 10. 1177/ 00420 98018 80613
World Economic Forum (2022) This chart shows the impact rising
urbanization will have on the world. Cities and Urbanization.
https:// www. wefor um. org/ agenda/ 2022/ 04/ global- urban izati on-
mater ial- consu mption/. Accessed 12 Jan 2023
Yang M, Chen L, Wang J, Msigwa G, Osman AI, Fawzy S, Rooney
DW, Yap PS (2022) Circular economy strategies for combating
climate change and other environmental issues. Environ Chem
Lett. https:// doi. org/ 10. 1007/ s10311- 022- 01499-6
Zhang S, Li X, Chen Z, Ouyang Y (2022) A bibliometric analysis of
the study of urban green spaces and health behaviors. Front Pub-
lic Health. https:// doi. org/ 10. 3389/ fpubh. 2022. 10056 47
Zope R, Vasudevan N, Arkatkar SS, Joshi G (2019) Benchmarking: a
tool for evaluation and monitoring sustainability of urban trans-
port system in metropolitan cities of India. Sustain Cities Soc
45:48–58. https:// doi. org/ 10. 1016/j. scs. 2018. 11. 011
Publisher's Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
Authors and Aliations
KristijanBrglez1,2· MatjažPerc1,3,4,5· RebekaKovačičLukman1,2
* Rebeka Kovačič Lukman
rebeka.kovacic@um.si
1 Faculty ofNatural Sciences andMathematics, University
ofMaribor, Koroška c. 160, 2000Maribor, Slovenia
2 Faculty ofLogistics, University ofMaribor, Mariborska c. 7,
3000Celje, Slovenia
3 Complexity Science Hub Vienna, Josefstädter Straße 39,
1080Vienna, Austria
4 Department ofMedical Research, China Medical University
Hospital, China Medical University, Taichung, Taiwan
5 Department ofPhysics, Kyung Hee University, 26
Kyungheedae-ro, Dongdaemun-gu, Seoul, RepublicofKorea
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1.
2.
3.
4.
5.
6.
Terms and Conditions
Springer Nature journal content, brought to you courtesy of Springer Nature Customer Service Center GmbH (“Springer Nature”).
Springer Nature supports a reasonable amount of sharing of research papers by authors, subscribers and authorised users (“Users”), for small-
scale personal, non-commercial use provided that all copyright, trade and service marks and other proprietary notices are maintained. By
accessing, sharing, receiving or otherwise using the Springer Nature journal content you agree to these terms of use (“Terms”). For these
purposes, Springer Nature considers academic use (by researchers and students) to be non-commercial.
These Terms are supplementary and will apply in addition to any applicable website terms and conditions, a relevant site licence or a personal
subscription. These Terms will prevail over any conflict or ambiguity with regards to the relevant terms, a site licence or a personal subscription
(to the extent of the conflict or ambiguity only). For Creative Commons-licensed articles, the terms of the Creative Commons license used will
apply.
We collect and use personal data to provide access to the Springer Nature journal content. We may also use these personal data internally within
ResearchGate and Springer Nature and as agreed share it, in an anonymised way, for purposes of tracking, analysis and reporting. We will not
otherwise disclose your personal data outside the ResearchGate or the Springer Nature group of companies unless we have your permission as
detailed in the Privacy Policy.
While Users may use the Springer Nature journal content for small scale, personal non-commercial use, it is important to note that Users may
not:
use such content for the purpose of providing other users with access on a regular or large scale basis or as a means to circumvent access
control;
use such content where to do so would be considered a criminal or statutory offence in any jurisdiction, or gives rise to civil liability, or is
otherwise unlawful;
falsely or misleadingly imply or suggest endorsement, approval , sponsorship, or association unless explicitly agreed to by Springer Nature in
writing;
use bots or other automated methods to access the content or redirect messages
override any security feature or exclusionary protocol; or
share the content in order to create substitute for Springer Nature products or services or a systematic database of Springer Nature journal
content.
In line with the restriction against commercial use, Springer Nature does not permit the creation of a product or service that creates revenue,
royalties, rent or income from our content or its inclusion as part of a paid for service or for other commercial gain. Springer Nature journal
content cannot be used for inter-library loans and librarians may not upload Springer Nature journal content on a large scale into their, or any
other, institutional repository.
These terms of use are reviewed regularly and may be amended at any time. Springer Nature is not obligated to publish any information or
content on this website and may remove it or features or functionality at our sole discretion, at any time with or without notice. Springer Nature
may revoke this licence to you at any time and remove access to any copies of the Springer Nature journal content which have been saved.
To the fullest extent permitted by law, Springer Nature makes no warranties, representations or guarantees to Users, either express or implied
with respect to the Springer nature journal content and all parties disclaim and waive any implied warranties or warranties imposed by law,
including merchantability or fitness for any particular purpose.
Please note that these rights do not automatically extend to content, data or other material published by Springer Nature that may be licensed
from third parties.
If you would like to use or distribute our Springer Nature journal content to a wider audience or on a regular basis or in any other manner not
expressly permitted by these Terms, please contact Springer Nature at
onlineservice@springernature.com