Abstract
This article presents a systematic review of empirical studies on polycentric spatial structures at a regional scale in order to assess their effectiveness as prescriptive and normative models in spatial planning. The results show that very few studies have emphasised primarily the positive effects of polycentricity, while a large number have evaluated the performance of non-polycentric (monocentric) structures more positively. Our study shows that evaluating the effectiveness of polycentricity as a normative model is both theoretically and empirically challenging, and that polycentricity is still the subject of a research agenda with hypotheses that need to be tested. The findings indicate that polycentricity is not the superior model it has been frequently advertised as and that its effectiveness is significantly influenced by a range of factors relating to its political foundation, weak theoretical positioning, ambiguous conceptualisation, context dependence, and highly variable governance frameworks. The study recommends that scientific theorising of polycentricity should be aligned with close scrutiny of the relevant contexts to overcome its idealistic nature and lack of adaptability. The article cautions planners and policymakers against a sweeping promotion of polycentric development, as the implementation of this concept is not necessarily associated with fostering economic performance, social cohesion, and environmental sustainability.
Introduction
Over the last two decades, the utilisation of the concepts of “polycentrism”1 and “polycentric development” has noticeably increased in the strategies and plans of spatial development (Meijers, 2008a, Wang et al., 2022). These concepts have been recognised as key elements and served as both a scientific analytical framework for examining real-world phenomena and the politically important parts of normative goals and perspectives in spatial development policies (Harrison and Hoyler, 2014, Lambregts, 2009, Derudder et al., 2022, Hall and Pain, 2006, Taylor et al., 2008). To achieve objectives such as enhancing economic performance, promoting social cohesion, and advancing environmental sustainability, these concepts have been integrated into spatial development policies and plans at different levels (Burger and Meijers, 2012, Zhang et al., 2022). Historical recovery shows that the emergence of the concept of polycentricity in the 1990 s to promote the benefits of “European integration” is a significant departure from traditional approaches in spatial planning. In particular, the European Spatial Development Perspective Document (ESDP) introduced a new framework for considering the spatial organisation of cities and regions. ESDP advocates for the first time a balanced spatial structure that fosters cooperation and complementarity between cities and regions. This normative interpretation from polycentricity made it the most desirable model of spatial structure and a leading principle in achieving balanced regional development throughout the EU, making it the main objective of EU regional policy. Today, polycentric conflict remains a central theme in EU territorial cohesion policy, and its popularity has spread even beyond Europe. This concept in normative interpretation promises to reduce spatial inequalities, combat the negative effects of excessive concentration and social-spatial polarization, and increase the competitiveness and efficiency of economic production regardless of the spatial context. However, the popularity of the concept of polycentricity has led to its acceptance in planning circles, and its vague and ambiguous meanings have caused confusion and uncertainty in the conceptualization of polycentric development in the planning apparatus. Simultaneous polycentricity has quickly attracted the attention of academic circles and has become an important research topic. This issue has caused controversy between the scientific and political discourse of polycentricity. On one side, the absence of robust empirical evidence has led some researchers to concentrate on the potential and theoretical aspects of polycentricity rather than empirical facts and theories (Groth et al., 2011). On the other, politicians have established the foundation for the practical introduction of these concepts into countries' spatial planning documents by giving their approval. Planners and politicians, inspired by the adoption of polycentricity as a role model in certain regions, have taken active measures to implement it in other contexts through public intervention. Some researchers adopt a more cautious viewpoint to the claimed positive functions of polycentricity, opting to thoroughly evaluate the empirical evidence before reaching any conclusions. Viewing it as a matter of concern, Davoudi (2007), Meijers and Sandberg (2008), and Li et al. (2022a) have expressed their criticism of the political endorsement of polycentricity as a panacea for all problems. They posit that polycentricity may simply serve as a placebo, which could mean anything and potentially act as a pathogen, exacerbating existing problems. While polycentricity theoretically asserts to improve economic performance, enhance social cohesion, and promote environmental sustainability, these claims have yet to be substantiated through empirical evidence (Davoudi, 2003, Manole et al., 2020, Parr, 2004, Rauhut, 2017; B. A. S. Waterhout et al., 2005; W. Li, Sun, et al., 2018; Natalia & Heinrichs, 2020).
Despite researchers' involvement, the absence of theoretical perspectives to support polycentric development as a normative policy stance remains an issue. Its effects are also uncertain from an empirical viewpoint (Agarwal et al., 2012, Rauhut, 2017, Vandermotten et al., 2008). The questionability of polycentric development's multi-objective nature as a spatial planning key concept is apparent. The examination of the social, economic, and environmental impacts of polycentricity, including both potential advantages and drawbacks, has been insufficiently addressed or overlooked. The significance of this issue lies in the recognition of polycentricity as a desirable and normative model for spatial development, as it has the potential to serve as a guiding principle for political intervention (Cheng and Shaw, 2018, Rauhut, 2017, Waite, 2023). Camagni and Capello (2004) maintain that polycentricity can only be regarded as a new paradigm in spatial sciences when its exact meaning is fully defined, its theoretical economic logic is justified, and its empirical characteristics are distinguished from traditional spatial realities and processes. Davoudi (2003) believes that failing to promote and understand polycentricity as a model for spatial development will result in it becoming just another “idea” and not a sustainable model. Thus, to ensure its sustainability, polycentric development must undergo testing to determine its usefulness and validity (Meijers, 2008a). The idea of polycentricity is intricate, just like TV series that need a complex blend of strong storytelling, engaging characters, high production standards, skilled actors and agents, innovation, effective marketing, and critical acclaim to be successful. Polycentricity is akin to TV series in the sense that various factors are crucial and must be present for it to succeed. Consequently, supporting polycentricity based solely on idealistic and positive objectives is inadequate, as weak links in any of the necessary factors may lead to its failure. Thus, to maximise the potential of polycentric development in spatial planning, it's crucial to assess its implications and adopt well-informed versions of it instead of blindly copying it.
In the academic literature, the term “polycentric urban regions” (PURs) refers to a manifestation of the scaling of urban development and the formation of “regional urbanisation.” (Soja, 2015). These new spatial structures result from the merger of adjacent cities of similar size, which were previously separate but interlinked (Burger and Meijers, 2012, Meijers et al., 2018). PURs are characterised by a regional spatial structure in which multiple urban areas interact and cooperate (Brezzi & Veneri, 2015). These regions exhibit interdependent economies, labour markets, and shared infrastructures; thereby, they transform the constituent settlements into “overarching entities” through their connections (Liu et al., 2016). The prevalence of functional relationships between cities, such as the development of agglomeration economies and the absence of diseconomies associated with more concentrated forms of development, such as congestion and environmental pollution, contribute to the growing prominence of PURs. Additionally, the pursuit of more sustainable and balanced urban development across cities further supports the organisation of urban systems in a polycentric manner (Van den Berghe et al., 2022). Therefore, the promotion of PURs is seen as a means to improve economic performance, promote social cohesion, and enhance environmental sustainability.
The examination of polycentric urban structures on this scale has garnered attention from several researchers in the field. This has resulted in an increased focus on investigating the characteristics and impacts of such spatial structures. These evaluations offer a valuable contribution to the ongoing debate surrounding polycentric urban structures. However, the question of whether polycentricity is a desirable spatial structure remains unresolved, and obtaining answers to these fundamental and supplementary questions is crucial for informed political decision making (Li and Liu, 2018, Meijers and Burger, 2010, Zhang et al., 2017). In light of these considerations, the present study aims to systematically review the empirical evidence on polycentricity on a regional scale. It endeavours to answer two questions: 1) Does empirical evidence support the notions about the effectiveness of polycentric urban structures in terms of achieving their intended goals on a regional scale? 2) What factors influence the effectiveness of polycentricity as a prescriptive and normative model? To put it simply, this study's second question investigates the effectiveness of the prescriptive and normative model "polycentricity." Effectiveness in this sense is measured by how well the model achieves its predetermined goals and objectives in real-world scenarios. Evaluating the degree of effectiveness involves assessing the model's alignment with the values and requirements of stakeholders; how effectively it addresses the challenges and opportunities of the planning context; and how efficiently it achieves its intended outcomes. To put it in a different way, this study aims to make a novel contribution to the field by tackling two main objectives. First, it aims to explore the impact of polycentricity on economic performance, social cohesion, and environmental sustainability. Second, it conducts a critical evaluation of the factors that influence the effectiveness of polycentricity as a prescriptive and normative model in spatial planning. To this end, it conducts an in-depth examination of various perspectives to systematically outline and examine the potential of polycentricity to advance economic, social, and environmental progress, or alternatively, to determine why it may not be successful in doing so.
The study is structured as follows: Section 2 offers an overview of the literature review, followed by the explanation of the methodology in Section 3. Section 4 presents the analyses, which will be discussed in Section 5. Finally, Section 6 presents the conclusion.
Section snippets
Literature review
The concept of PURs can be viewed as a product of an ongoing global discourse among scholars in the fields of urban planning and geography, dating back several decades into the 20th century. It has been argued that the polycentric spatial structures are becoming the leading form of city-regions in the new millennium (Bartosiewicz and Marcinczak, 2022, Dieleman and Faludi, 1998, Kloosterman and Musterd, 2001, Phelps and Ozawa, 2003, Van Houtum and Lagendijk, 2001). Van Meeteren (2022) sheds
Material and methods
The study at hand sets out to gather empirical evidence of the effects of polycentricity and to evaluate the factors affecting the effectiveness of polycentricity as a prescriptive and normative model. This is accomplished through conducting a systematic literature review, which serves as the first endeavour to organise and consolidate the existing knowledge and to provide relevant insights to researchers, planners, and policymakers (Fink, 2014). The systematic literature review is a rigorous
Polycentricity and economic performance
The evaluations of polycentricity that are deemed most critical are often linked to economic performance. Theoretical logic suggests that transitioning from monocentricity to polycentricity in urban regions may lead to a higher economic performance, and researchers have attempted to establish this by constructing empirical evidence. To evaluate the impact of agglomeration economies on local labour productivity, most studies adopt models based on the Cobb-Douglas production function (Ciccone,
Discussion
This article aims to conduct a systematic review of the evaluations of polycentricity in the intercity (regional) scale and to critically analyse the factors affecting its effectiveness as a prescriptive and normative key model in spatial planning. The empirical studies in this field have analysed various aspects, including economic performance, environmental sustainability, social cohesion, and multi-objective evaluations. The selected studies were categorised into four groups: positive,
Conclusion
Contemporary spatial planning recognises polycentricity as a fundamental principle. Policymakers have emphasised the transformation of the concept of polycentricity from a mere descriptive and analytical model into a prescriptive and normative model aimed at promoting economic performance, social cohesion, and environmental sustainability. With the objective of assessing the evaluation of polycentric spatial structures at the regional scale through empirical evidence and determining the factors
CRediT authorship contribution statement
Hashem Dadashpoor: Conceptualization, Methodology, Writing – original draft, Writing – review & editing, Supervision. Abbas Doorudinia: Conceptualization, Methodology, Investigation, Writing – original draft. Abolfazl Meshkini: Conceptualization, Writing − review & editing.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgment
We would like to express our sincere appreciation and respect to the esteemed editor, Karl Fischer and anonymous reviewers for their diligent and thorough review of our manuscript. Their invaluable guidance and constructive feedback have significantly improved the quality of our work.
Hashem Dadashpoor is an associate professor at Tarbiat Modares University, Faculty of Art and Architecture, Department of Urban and Regional Planning. His research interests include urban and regional planning, urban and regional studies, spatial planning, land use planning, and planning theory.
References (362)
S. Angel et al.
The productivity of American cities: How densification, relocation, and greater mobility sustain the productive advantage of larger U.S. metropolitan labor markets
Cities
(2016)
B. Bartosiewicz et al.
Investigating polycentric urban regions: Different measures – Different results
Cities
(2020)
J.C. Brinkman
Congestion, agglomeration, and the structure of cities
Journal of Urban Economics
(2016)
M. Brülhart et al.
Agglomeration and growth: Cross-country evidence
Journal of Urban Economics
(2009)
D. Burgalassi et al.
Urban spatial structure and environmental emissions: A survey of the literature and some empirical evidence for Italian NUTS 3 regions
Cities
(2015)
M.J. Burger et al.
Heterogeneous development of metropolitan spatial structure: Evidence from commuting patterns in English and Welsh city-regions, 1981–2001
Cities
(2011)
R. Camagni et al.
The City Network Paradigm: Theory and Empirical Evidence
(2004)
D. Castells-Quintana
Malthus living in a slum: Urban concentration, infrastructure and economic growth
Journal of Urban Economics
(2017)
O. Cats et al.
Multi-modal network evolution in polycentric regions
Journal of Transport Geography
(2021)
J. Chen et al.
City size and urban labor productivity in China: New evidence from spatial city-level panel data analysis
Economic Systems
(2017)