Overcoming the Subject-Object Dichotomy in Urban Modeling: Axial Maps as Geometric Representations of Affordances in the Built Environment

Abstract

The world is witnessing unprecedented urbanization, bringing extreme challenges to contemporary practices in urban planning and design. This calls for improved urban models that can generate new knowledge and enhance practical skill. Importantly, any urban model embodies a conception of the relation between humans and the physical environment. In urban modeling this is typically conceived of as a relation between human subjects and an environmental object, thereby reproducing a humans-environment dichotomy. Alternative modeling traditions, such as space syntax that originates in architecture rather than geography, have tried to overcome this dichotomy. Central in this effort is the development of new representations of urban space, such as in the case of space syntax, the axial map. This form of representation aims to integrate both human behavior and the physical environment into one and the same description. Interestingly, models based on these representations have proved to better capture pedestrian movement than regular models. Pedestrian movement, as well as other kinds of human flows in urban space, is essential for urban modeling, since increasingly flows of this kind are understood as the driver in urban processes. Critical for a full understanding of space syntax modeling is the ontology of its' representations, such as the axial map. Space syntax theory here often refers to James Gibson's “Theory of affordances,” where the concept of affordances, in a manner similar to axial maps, aims to bridge the subject-object dichotomy by neither constituting physical properties of the environment or human behavior, but rather what emerges in the meeting between the two. In extension of this, the axial map can be interpreted as a representation of how the physical form of the environment affords human accessibility and visibility in urban space. This paper presents a close examination of the form of representations developed in space syntax methodology, in particular in the light of Gibson's “theory of affordances.“ The overarching aim is to contribute to a theoretical framework for urban models based on affordances, which may support the overcoming of the subject-object dichotomy in such models, here deemed essential for a greater social-ecological sustainability of cities.

Full text

ORIGINAL RESEARCH
published: 20 April 2018
doi: 10.3389/fpsyg.2018.00449
Frontiers in Psychology | www.frontiersin.org 1April 2018 | Volume 9 | Article 449
Edited by:
Marketta Kyttä,
Aalto University, Finland
Reviewed by:
Enric Pol,
Universitat de Barcelona, Spain
Christopher M. Raymond,
Swedish University of Agricultural
Sciences, Sweden
*Correspondence:
Lars Marcus
lars.marcus@chalmers.se
Specialty section:
This article was submitted to
Environmental Psychology,
a section of the journal
Frontiers in Psychology
Received: 13 September 2017
Accepted: 19 March 2018
Published: 20 April 2018
Citation:
Marcus L (2018) Overcoming the
Subject-Object Dichotomy in Urban
Modeling: Axial Maps as Geometric
Representations of Affordances in the
Built Environment.
Front. Psychol. 9:449.
doi: 10.3389/fpsyg.2018.00449
Overcoming the Subject-Object
Dichotomy in Urban Modeling: Axial
Maps as Geometric Representations
of Affordances in the Built
Environment
Lars Marcus*
Spatial Morphology Group, Architecture and Civil Engineering, Chalmers University of Technology, Gothenburg, Sweden
The world is witnessing unprecedented urbanization, bringing extreme challenges to
contemporary practices in urban planning and design. This calls for improved urban
models that can generate new knowledge and enhance practical skill. Importantly,
any urban model embodies a conception of the relation between humans and the
physical environment. In urban modeling this is typically conceived of as a relation
between human subjects and an environmental object, thereby reproducing a humans-
environment dichotomy. Alternative modeling traditions, such as space syntax that
originates in architecture rather than geography, have tried to overcome this dichotomy.
Central in this effort is the development of new representations of urban space, such
as in the case of space syntax, the axial map. This form of representation aims to
integrate both human behavior and the physical environment into one and the same
description. Interestingly, models based on these representations have proved to better
capture pedestrian movement than regular models. Pedestrian movement, as well as
other kinds of human flows in urban space, is essential for urban modeling, since
increasingly flows of this kind are understood as the driver in urban processes. Critical
for a full understanding of space syntax modeling is the ontology of its’ representations,
such as the axial map. Space syntax theory here often refers to James Gibson’s “Theory
of affordances,” where the concept of affordances, in a manner similar to axial maps,
aims to bridge the subject-object dichotomy by neither constituting physical properties
of the environment or human behavior, but rather what emerges in the meeting between
the two. In extension of this, the axial map can be interpreted as a representation of how
the physical form of the environment affords human accessibility and visibility in urban
space. This paper presents a close examination of the form of representations developed
in space syntax methodology, in particular in the light of Gibson’s “theory of affordances.“
The overarching aim is to contribute to a theoretical framework for urban models based
on affordances, which may support the overcoming of the subject-object dichotomy in
such models, here deemed essential for a greater social-ecological sustainability of cities.
Keywords: space syntax, affordances, urban modeling, sustainable urban design, spatial cognition

Marcus Urban Models Based on Affordances
INTRODUCTION: THE
HUMANS-ENVIRONMENT RELATION IN
URBAN MODELING
The world is witnessing unprecedented urbanization (United
Nations, 2014), bringing extreme challenges to contemporary
practices in urban planning and design. This calls for improved
urban models that can generate new knowledge and enhance
practical skill. Importantly, any urban model embodies a
conception of the relation between humans and the physical
environment. In urban modeling this is typically conceived of as
a relation between human subjects and an environmental object
(Wilson, 2000), thereby reproducing a humans-environment
dichotomy.
Alternative modeling traditions, such as space syntax (Hillier
and Hanson, 1984) that originates in architecture rather than
geography, have tried to overcome this dichotomy. Central in
this effort is the development of new representations of urban
space, such as in the case of space syntax, the axial map1
(Hillier and Hanson, 1984). This form of representation aims
to integrate both human behavior and the physical environment
into one and the same description. Interestingly, models based
on these representations have proved to better capture vehicular
and pedestrian movement than regular models (Hillier and Iida,
2005). Such movement, as well as other kinds of human flows in
urban space, is essential for urban modeling, since increasingly
flows of this kind are understood as drivers in urban processes
(e.g., Batty, 2013).
Critical for a full understanding of space syntax modeling
is the ontology of its’ representations, such as the axial map
discussed below. The issue has given rise to several approaches
in the space syntax literature, that not are immediately
congruent. Through the years, there has been aims to view these
representations from the point of view of phenomenological
geography (e.g., Seamon, 2007), systems biology (Griffiths and
Quick, 2005), neuroscience (e.g., Sakellaridi et al., 2015), or
spatial cognition (Conroy Dalton et al., 2012). While this
discussion remains inconclusive, there has also been a more
technical debate, propelled by the rapid increase in accessible
geodata on the internet (Stavroulaki et al., 2017). Essential here
is the shift from Axial maps drawn by hand in GIS to maps
based on Road Center Lines downloaded from, for instance,
Open Street Map or different national road authorities. While
this primarily has been driven by convenience, in that it is less
time consuming to download a road system than to draw one
yourself, and by incentives to adapt to other directions in urban
modeling, where this is standard procedure, it again highlights
the issue of the ontology of these representations. Moreover, there
has been several proposals from within the space syntax field
about how the axial map could be improved. One may identify
four major directions here, (1) Angular Segment Analysis (e.g.,
Turner, 2007); (2) Natural Streets maps (Jiang and Claramunt,
1We will only refer to the axial map here, while keeping in mind the general
implications of our argument for other geometric representation typical for
space syntax, such as the segment map or the isovist. For full review of these
representations, see Stavroulaki et al. (2017).
2002); (3) Continuity maps (Figueiredo and Amorim, 2005); and
(4) Directional Distance models (Peponis et al., 2008). These
directions are thoroughly analyzed and compared in Stavroulaki
et al. (2017).
Altogether, however, this leaves the status of the ontology of
the representations in space syntax unsettled, where we by this
simply mean; we do not quite know what they represent. To
simply state that they are representations of space, or space as
structured by built form, in the end leaves the issue far too open.
Put differently, although we repeatedly see powerful correlations
between analyses of the built environment based on space syntax
representations and human behavior, especially movement, we
do not have a theory that help us understand why this is so. This
in turn hinders conscious improvements of the representations
and ultimately also precision in the translations of these findings
into policy and practice.
In this paper, we aim to remedy this by returning to the axial
map, which we deem a highly original form of representation
with a potentially strong foundation in psychological theory, in
particular James Gibson’s theory of affordances (1977), which
we believe can shed light also on the ontological status of more
recent development of the axial map, such as segment maps, as
well as ready-mades, such as road center lines. Gibson’s theory
of affordances has often been referred to in the space syntax
literature (e.g., Hanson, 2000), yet his broader theory about An
Ecological Approach to Human Perception (1986), of which his
affordance theory is part, has never been thoroughly discussed in
relation to space syntax theory, despite the great affinity between
the two theories on the matter of the humans-environment
relation. Ultimately, we propose that Gibson offers a theory
that help us understand why space syntax modeling works and
that space syntax offers modeling techniques that make Gibson’s
theories operative on the scale of the city.
Hence, if this affinity can be substantiated into a distinct
link, it may prove vital, both from the point of view of urban
modeling, aiming to inform practices in urban planning and
design, and environmental psychology, aiming to understand the
relation between human behavior and the physical environment,
and that in several respects. First, it opens for models that
capture how human behavior is conditioned by the environment,
which offers the opportunity to also model and understand how
interventions of the built environment may influence human
behavior. Second, it opens for models that capture how the
same physical environment gives rise to different affordances
depending on variations in the physical ability among humans,
relating for instance to physical disabilities or age, but also, how
the same physical environment gives rise to different affordances
relating to other species than humans, such as birds or bees.
Finally, it opens for combining affordances relating to both
humans and other species in urban environments, which would
substantially broaden the capacity of urban planning and design
when it comes to transforming cities into greater social-ecological
sustainability.
Hence, this paper aims to contribute to a stronger theoretical
foundation of the form of representations developed in space
syntax methodology, such as the axial map, by way of a close
reading of Gibson’s theories about affordances and ecological
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Marcus Urban Models Based on Affordances
space, which also is intended as an argument for space
syntax modeling as an approach that in contrast to much
urban modeling bridges the humans-environment dichotomy. In
extension, the aim is to also introduce to psychological theory a
strand of urban modeling directly linked to important directions
in psychology. We deem both important in the light of the
shared aim of the two fields to create greater social-ecological
sustainability in cities.
SPACE SYNTAX: AN ARCHITECTURAL
APPROACH TO THE
HUMANS-ENVIRONMENT RELATION
The central components of any urban model are a set of modes
to measure the key variables distance and attraction within a
representation of urban space (Wilson, 2000). Distance can here
be measured in many different ways, for instance as metric
and temporal distance or as economic cost; attractions may be
measured as anything from density of residents or accessibility
to retail or parks. Similarly, urban space may be represented in
many different manners, but the most common are either as
coordinates in continuous space or as patterns of discrete spaces,
for instance census tracts (Wilson, 2000). The issue of spatial
representation becomes particularly interesting if we shift from a
geographical to an architectural conception of space, since we in
the latter find interesting alternatives, not least in what is known
as space syntax research (Hillier and Hanson, 1984).
Space syntax origins in the 1970’s debate about the need for
sounder knowledge foundations for the design of new housing
areas (Hillier et al., 1976). The background was the severe
criticism of the ambitious British social housing program of the
1960’s, where these, if anything, seemed to create social problems
rather than remedy them. Similar criticism could be found
throughout the western welfare states in the early 1970’s. In most
cases it embodied the same paradox: when the social ambitions
had been the highest, architecture had failed the greatest.
An early contribution to this aim from the main originator
of space syntax theory, Bill Hillier, concerned a critique of
the established conception of the humans-environment relation
(Hillier and Leaman, 1973). This line of argument was again
taken up by Hillier in Space is the Machine (1996), which we here
will follow closely in the aim to both identify the foundations of
space syntax theory in this respect, but also in the aim to closer
tie space syntax theory to Gibson’s conception of embedded
cognition.
Hillier follows Canguilhem (1971) in identifying the origin
of the environment concept in emerging disciplines like biology
and zoology in the seventeenth century (Hillier, 1996). The
central issue here was to explain the great variety of species
on Earth, where one, following the ideal of physics, looked for
material explanations. The idea evolved that this was a result of
the environment, typically conceptualized in a rather awkward
mechanistic way that later often has been ridiculed. Hillier argues
that this idea, even so, lived on into the twentieth century in
architecture, translated into a paradigm of the machine; the idea
that architecture through its’ materiality somehow is able to
influence, change and direct individual behavior. He in particular
points out how a central problem here is how this idea reinforces
the subject-object duality: “This blinds the inquirer to the most
significant single fact about the built environment: that it is
not simply a background to social behavior—it is itself a social
behavior” (Hillier, 1996, p. 300). The reason it can be seen as such,
according to Hillier, is that the built environment not is a natural
environment, it is an artifact, and as such shaped according to
basic human abilities with the very aim to condition and direct
human behavior.
It is important to recognize the two-front character of the
argument pursued here. At heart, space syntax springs from
a critique of social engineering, architectural determinism and
the paradigm of the machine, but it does not abandon either
a belief in positive knowledge or a systematic relation between
space and society, as much of the 1970’s critique did. Hillier
means that the latter critique led to a decisive change in
architectural research from analytical studies of function, to
hermeneutical studies of meaning, that is, an altogether different
topic, somewhat mirroring the debate between behavioral and
cognitive approaches in psychology (e.g., Sörqvist, 2016). In
short, Hillier and Hanson want to save the idea that architecture
has social effects, cognitively through the reading of architectural
signs as well as behaviorally through the use of spatial form, by
the means of a new and better scientific paradigm, where the
critical difference from the earlier one is a shift from theory
based on a direct relation between the physical environment
and humans, to one where this relation is mediated by spatial
configurations.
The central argument here is that human use of space must
be understood dynamically, that is, through human movement
in space rather than as static uses in particular spaces. This put
emphasis on the relation between spaces, their configuration,
rather than the physical form of individual spaces per se—we see
the reason for the name space syntax. This, next, leads to the
observation that in real life different human uses typically overlap
in space rather than stick to particular spaces. Hillier and Hanson
call this a non-correspondence relation between space and use,
in contrast to the conventional correspondence relation between
the two (Hanson and Hillier, 1987). This means that human
use of space for movement has a vital and intermediate role in
relation to other human uses or social phenomena in urban space.
The configuration of space, as captured in the axial map, has
then in a long line of empirical tests proven to an important
degree structure movement patterns in urban space so that we
find different numbers of co-present people in different urban
spaces. This, in turn, create particular situations of varying social
and economic potential in these spaces, relating to such things
as social integration (e.g., Legeby, 2013) and local markets (e.g.,
Scoppa, 2015).
Importantly, such movement patterns are also essential
when it comes to the encounter between people and urban
green, central for changing people’s behavior and attachment to
environmental issues and improved sustainability (Marcus et al.,
2016). This happens in three ways. First, in that the configuration
of space structures movement so that it to greater or lesser extent
pass urban green areas. Second, in that these movement patterns
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Marcus Urban Models Based on Affordances
generate particular situations of co-presence in urban green areas
that become part of their experience—whether there are 2, 20, or
200 people co-present around a water pond in a park dramatically
changes its meaning. Third, in that depending on the size of these
co-presences the landscape design may change to create more
useful encounters between people and urban green. The two
latter emphasize how space syntax methodology also can address
symbolic and affective affordances and not only functional.
We may illustrate this with an example. Imagine a city where
everyone walks to work each morning, whether these people
encounter any form of urban green on their journeys, naturally
depends on the distribution of green areas in the city but also
on the configuration of the street network. Walking to work
normally implies simple and direct journeys, which according to
the arguments above, generally means streets of high centrality in
the street system, hence we need to distribute green areas along
these particular streets for such encounter to happen. In the next
step, however, this also means that green areas in these locations
will be frequently visited, that is, I normally will encounter the
green together with others and often with many others. This
creates a particular situation for the encounter with the green; it
is somehow “colored” by the large group of others. This naturally
does not mean that this is bad, but it is different from a situation
where you encounter the same green alone or together with few
other people.
The first case may also imply that one should design the urban
green in a particular way to accommodate for this particular
situation of quite few simultaneous visitors. For instance, large
groups of people mean a lot of wear and tear, why areas covered
with grass need certain treatment or perhaps even to be avoided,
not to present nature as something worn and dirty to visitors,
which then may come to prefer shopping malls with flower pots.
In contrast, more segregated space may be designed in a very
different manner and also have a different function for human
interaction with nature. There naturally are many dimensions to
this example, but in principle it demonstrates how movement
patterns and the situations of co-presence it generates is essential
for building a relation between humans and nature in cities,
where the point in our current discussion is that we can learn to
better model and understand these patterns through space syntax
models based on representations of certain human affordances.
Naturally, every step in this argument, while empirically
supported in many studies (e.g., Hillier and Iida, 2005), has
also been debated: from the representation of the axial map
itself (Batty, 2013), over to its distance measure (e.g., Jiang
and Claramunt, 2002), its statistical correlation with number
of co-present people (e.g., Ståhle et al., 2005), and the social
interpretation of these situations of co-presence (Liebst, 2014).
In relation to current urban development challenges, it also
demonstrates limitations, where major directions in need of
development concern, joining the axial map with other models
of urban mobility (Gil, 2016), incorporating also urban green
structures (Berghauser Pont et al., 2017), and extending the
models over time, allowing for dynamic analysis.
Hence, space syntax is a field still in development but
has introduced a novel and substantiated approach to the
humans-environment relation by way of spatial configuration:
“Spatial configuration proposes a theory in which we find pattern
effects from space to people and from people to space that in
no way invokes mechanistic determinism. At the same time, the
configuration paradigm saves the idea that architecture has social
effects. By changing the design of a building or complex we do
change outcomes. There is after all some kind of mechanism
between the built world and people. However, the machine is not
the building. Space is the machine” (Hillier, 1996., p. 300).
SPACE SYNTAX: CITIES AS COGNITIVE
OBJECTS
To understand how space may become a machine, we need to
better understand properties of space in relation to basic human
capacities and how humans by making use of these properties,
have rearranged the environment to their own purposes. Hillier
maintains that people interact with space in cities both through
their capacity as bodies and as minds and argues that: “in bodily
terms the city exist for us as a system of metric distances,” while
we mentally interact with it primarily by seeing: “as a system of
visual distances” (Hillier, 2012, p. 4). We here see the theoretical
foundations for the axial line, which simply is a geometric
representation of an urban space structured and limited by built
form, that is possible to physically access and visually overlook
for a generic human.
However, Hillier also argues that: “we also need to reflect
on the fact that cities are also collective artifacts which bring
together and relate very large collections of people. The critical
spatial properties of cities are not then just the relation of one
part to another, but of all parts to all others” (Hillier, 2012, p. 4).
Here we see the need to expand the axial line to an axial map,
which is a set of axial lines covering all spaces accessible for a
generic human within a spatial system structured and limited
by built form. As a means to measure distances within such a
system, Hillier next proposes the notion of universal distance as
opposed to specific distance (Hillier, 1996, p. 104–108). Where
specific distance concerns the distance between an origin A and
a destination B, universal distance concerns the distance from all
possible origins to all possible destinations in a spatial system.
Hence, universal distance comes close to the concept centrality,
for instance found in network analysis (Newman, 2010).
According to Hillier, universal distance behaves differently
from regular ideas about distance (Hillier, 2012, p. 5). He
illustrates by filling a bounded space with a set of rectangular
objects, resembling urban blocks, in such a way that the
remaining space takes a form that looks like a street grid
(Figure 1). By moving the blocks slightly, so that some of the
lines of sight are broken, Hillier shows how visual distances are
increased dramatically, while the metric distances changes only
marginally. This reflects the common experience that the same
metric distance can be experienced very differently depending on
the particular spatial situation; for instance, one can imagine how
trips in the second system will both take more time as well as
represent a greater effort than in the first system; that is, not a
much greater physical effort but a much greater mental effort.
The argument for the axial line as a distance unit can then
be made: If we make a straight line crooked “we do not add
significantly to the energy effort required to move along it,
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Marcus Urban Models Based on Affordances
FIGURE 1 | Analysis of universal visual distance in a grid-like bounded space, where small displacements of the blocks cause dramatic increase in universal visual
distance (Hillier, 2012).
but we do add greatly to the informational effort required”
(Hillier, 2003, p. 3). Based on the idea that cities, as products of
bottom-up incremental processes over long time (see Alexander,
1964), have tended to evolve toward environments that support
human intelligibility, Hillier concludes that: “human geometric
intuitions seem to be embedded in the city itself ” and in extension
that: “cities are in a profound sense cognitive—and so human—
objects before they are economic and social objects” (Hillier,
2012, p. 18). We may then, at least in part, also identify a possible
explanation to the failure of the large-sale housing programs of
the 1960’s, which typically did not evolve in relation to human
practice over large time spans, but rather were rapid large-scale
interventions, little informed about human cognition or use of
the environment.
On this basis, we can begin to more precisely understand
what the axial map represents (Figure 2). It is a representation
of continuous urban space, structured by built form such
as buildings, infrastructure and landscape elements, which
specifically captures a vital set of affordances (accessibility and
visibility) that the environment gives rise to in relation to a
moving human subject. It does so by representing urban space as
the least amount of straight (axial) lines that completely covers
the whole system under analysis. Hence, the axial map can be
interpreted as an attempt, with the simplest geometry possible, to
represent this set of affordances. Finally, each axial line can then
be used as a unit for topological measurement of distances, which
can be argued to be based in human perception and cognition.
We here see the essential importance in choice of geometric
representation in urban modeling, where the axial line in
this case, despite its’ mundane appearance, on the one hand,
constitutes a kind of cognitive geometry, in that it represents
the spatial environment (the object) from the point of view
of a perceiving and cognizing human (the subject), that is, a
representation that neither is a representation of the subject
or the object, but rather a representation that overcomes the
categorical separation of the two. On the other hand, this
representation opens for precise description, analysis, and even
quantification of this geometrically constructed entity. For
instance, we may topologically measure the number of axial
lines between two locations or, in the same manner, measure the
centrality of a location in a spatial system, which we in both cases
FIGURE 2 | The axial map as a representation of spatial.
may call an analysis of cognitive distance. It is this manner of
measuring distance, that is, as topological steps of axial lines in an
urban environment represented as an axial map, that in repeated
empirical investigations has proven to capture both pedestrian
and vehicular movement better than other distance measures
(e.g., Hillier and Iida, 2005).
SPACE SYNTAX: A COPERNICAN SHIFT IN
URBAN NETWORK ANALYSIS
When we come to analysis, axial maps and later developments
into segment maps etc. (see note 1), are all treated as networks,
and as such formally described by graphs and thereby part of a
long tradition of applying graph theory in spatial analysis and
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Marcus Urban Models Based on Affordances
urban modeling (Batty, 2013). A common procedure here is to
represent urban elements, such as buildings, parks, or retail, as
nodes and the relations between these as links in a network
matrix (Batty, 2013). When embedding such a network in a real
urban setting, however, one most often make use of the street
network for setting urban elements in spatial relations to each
other. When representing such street networks as graphs one
normally represents street-junctions as nodes and the street-
segments connecting these as links. Peculiar to the axial map,
however, is that this is done the other way around; streets are
represented as nodes and junctions as links. In formal graph
terms, there is always such a dual graph to a network, the mirror
image of the primal graph (Figure 3), and it is this dual graph that
is made use of in space syntax.
This procedure is logical to the conception of space we find in
space syntax, since it means that we represent urban space as a set
of spaces defined by a certain set of affordances (accessibility and
visibility), where each such space is represented as a node in the
graph and each junction of such spaces is represented as a link.
Representing the axial lines as nodes and the junctions between
axial lines as links, rather than the opposite, means that the
cognizing subject, so to speak, is shifted from the street-junctions
to the street-segments and, moreover, from being represented as
a point to being represented as a line. We propose that this has far
greater consequences than what it seems and actually constitutes
something of a Copernican shift in urban network modeling.
This is especially true, since what is represented by the axial
lines, as we have seen, are spaces possible for a human to
physically access and visually overlook, and such spaces are
normally not limited to the space of a street segment, but
regularly extend beyond such segments, while at times also being
shorter than a segment. This has the rather contradictory effect
that an axial line can be connected to several other axial lines,
while these lines, in turn, not are connected to each other. In
relation to human perception, however, this makes sense; even
though we in a physical sense are located at a specific point, we
may visually overlook a much larger area, potentially including
several street-junctions, and in that visual sense be present also at
these other street-junctions—the axial line in an original manner
captures both of these dimensions.
Hence, we see a different conception of space in space syntax
compared to regular urban modeling, a conception, we will
argue, comes very close to what Gibson has called an ecological
conception of space in contrast to the conception of space in
physics, which is what we normally encounter in urban modeling.
ECOLOGICAL SPACE: ENTERING THE
WORLD OF MEANINGFUL THINGS
Gibson’s particular point of departure is well-captured by the title
of his book: An Ecological Approach to Visual Perception (1986).
The term “ecological” marks a break with physicist conceptions
of the environment and point to our habit to speak about
reality as the physical world and, as a consequence, the risk of
uncritically adopting physicist conceptions of the environment.
In contrast to such conceptions he states the rather obvious fact
that from the point of view of psychology: “we are concerned here
with things at the ecological level, with the habitat of animals and
men” (Gibson, 1986, p. 9), which concerning our understanding
of space constitutes a subsection of physics, albeit a subsection we
need to understand better.
In Gibson’s own words, his theory “provides a counterbalance
to those theories of cognitive mapping that have focused mainly
or only on the internal cognitive processing of environmental
information, to the exclusion of any interaction of the individual
and the environment” (Gibson, 1986, p. 13). More precisely, he
wants to open for an understanding of the body as an extension of
the mind, together constituting an integrated perceptual system,
rather than a sequence where the one follows upon the other.
FIGURE 3 | The Copernican shift in graph representations of urban space in space syntax (Batty 2013). (A) The street network as an axial map. (B) The primal syntax
between streets/lines. (C) The dual syntax between junctions/points.
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Marcus Urban Models Based on Affordances
It also explains Gibson’s unwillingness to make a distinction
between perception and cognition. He argues: “Our reasons
for supposing that seeing something is quite unlike knowing
something come from the old doctrine that seeing something
is having temporary sensations one after another at the passing
moment of present time, whereas knowing is having permanent
concepts stored in the memory” (Gibson, 1986 p. 258).
Consequently, Gibson constructs a new ontology, based
in an ecological conception of the world rather than a
physical one. To give an example of what the difference here
implies, we can compare the isotropic conception of space
in physics, defined by an x, y, and z-axis, with ecological
space conceptualized as what surrounds living organisms, where
the latter immediately need to acknowledge the primacy of
the ground, for instance; for an experiencing human, there
simply is no spatial isotropism, the way physics tend to deal
with space. In Gibson’s words: “The world of physical reality
does not consist of meaningful things. The world of ecological
reality, as I have been trying to describe it, does” (Gibson,
1986 p. 33).
First of all, Gibson instigates the mutuality of animals, which
includes humans, and the environment, the fact that: “each
term implies the other” (Gibson, 1986 p. 8). This conception
of mutuality between animal an environment gives rise to the
basic elements of his ontology: medium,substances and the
surfaces that separate them, where the typical “media” are air
and water, which allow animal movement, while the earth,
and other hard materials that do not allow such movement,
are “substances.” Interfaces between these, whether between
different media or different substances or between a medium
and a substance, all constitutes “surfaces” (Gibson, 1986 p.
16). The latter plays a critical role for perception in that they
give structure to the light that surrounds us and thus allows
for vision. Gibson calls this ambient light, which maintains
its particular property from the fact that it concerns light
in an environment, which causes rays of light, even though
we assume a primary source of light such as the sun, to
continuously reflect so that we can think of them as coming
from every direction, thus filling the medium. However, this
also implies that an environment, constituted by a particular
configuration of surfaces, typically will structure the ambient
light in a certain way and give rise to what Gibson calls
an ambient optic array that, in principle, is unique for every
location (Gibson, 1986 p. 51). It is this structured array of
light that enables light to carry information that can specify the
environment for a perceiving animal, that is, that light from a
point of observation simply will have different forms in different
directions.
Of specific importance to architecture and urban design is
Gibson’s discussion about how the structure and shape of the
environment creates what he famously has called affordances
(Gibson, 1986 pp. 127–143). This concerns how a given
environment affords, that is, presents certain potentials for
behavior depending on the constitution of the bodies of different
animals: “The affordances of the environment are what it offers
the animal, what it provides or furnishes, either for good or for
ill” (Gibson, 1986 p. 127). While we primarily may think of
affordances as given by the natural environment it is obvious
that many species, not only humans, invest a lot of energy and
resources into transforming the environment according to their
purposes, that is, they transform the environment to increase its
affordance in relation to the needs of their own species. As Gibson
notes (Gibson, 1986 p. 37), this can also concern the creation
of obstacles in the environment, a form of “disaffordance,” to
protect from or exclude other species. When it comes to the
human species, such investments in affordances have taken on
tremendous proportions transforming large parts of the Earth’s
surface.
Gibson’s shift toward a conception of the mind and the body
as an integrated perceptual system also implies that movement
is essential to any kind of perception; from the movement of
the eye balls in the head, over to the movement of the head at
the top of the neck, to the movement of the body through the
environment by means of walking: “Vision is a whole perceptual
system”; in short, even though: “one surely looks with the eyes
[...] one does not see with the eyes” (Gibson, 1986 p. 205). With
the idea of the body as a perceptual system, Gibson makes a
decisive break with conventional cognitive science, especially as
developed in neuro science, where the body and the head in many
experiments, at least traditionally, were forced to keep still in
the aim to investigate the brains reaction to different controlled
stimuli. His point here is that these experiments may be useful if
we want to understand how the brain works, but they are not
realistic if we want to understand how humans perceive their
environment. In the latter case movement is essential, and in the
end what distinguishes animals from other organisms is that they
can move—it is their competitive advantage.
Human movement, especially bodily locomotion, is what
sets Gibson’s ontology into action, so to speak. The medium
affords human locomotion but is structured by substances. The
substances, however, are not mere obstacles but offer permanence
against which movement can be sensed and controlled. More
specifically this happens through the changing configuration
of surfaces that continuously come into and move out of the
field of vision, hence structuring and restructuring the ambient
light which thereby carries information about the environment
to the perceiving human. From the information point of view
the tension between change through human locomotion and
permanence offered by the environment is critical: “The optic
array changes, of course, as the point of observation moves. But
it also does not change, not completely. Some features of the
array do not persist and some do. The changes come from the
locomotion, and the non-changes come from the rigid layout of
the environmental surfaces. Hence, the non-changes specify the
layout and count as information about it; the changes specify
locomotion and count as another kind of information, about
the locomotion itself” (Gibson, 1986 p. 73). As a matter of
fact, all individual perception is in this sense continuous, why
each moment of perception, in principle, happens against the
background of earlier moments of perception, why these are part
of the present moment of perception. We simply cannot exclude
memory from perception and, therefore, the distinct divide
between perception and cognition proves difficult to sustain,
according to Gibson.
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Marcus Urban Models Based on Affordances
If we acknowledge the fact that humans primarily perceive the
environment under movement and that arrested vision rather is
the limiting case, this proves to have quite radical implications.
First, as we have seen, that the past somehow is present in
the present, so to speak; what we just saw help us perceive
what we see now, that is, that we cannot discount memory
in perception. While this manner of understanding perception,
hence, dislocates the moment of observation, as it were, it
similarly, second, also dislocates the location of observation:
“Seeing the world at a traveling point of observation, over a
long enough time for a sufficiently extended set of paths, begins
to be perceiving the world at all points of observation, as if
one could be everywhere at once” (Gibson, 1986 p. 197). While
this at first seems to be an odd conclusion, upon reflection it
seems to be a rather apposite description. What we perceive
when we move around the environment cannot really be said
to be a series of images of this environment, but rather a
complete conception of that environment, however imperfect,
where certain parts stand out more than others, that is, closer to a
3D-model.
COGNITIVE GEOMETRY: REPRESENTING
HUMAN-ENVIRONMENT RELATIONS AS
THINGS
We clearly see connections between the two conceptions
of the relation between humans and the environment
in the two discussions above; space syntax looking for
powerful representations that capture humans embedded
in the environment and Gibson identifying affordances as an
immediate link between humans and the environment. Most
interestingly in this respect, Gibson states: “An observer who is
getting around in the course of daily life sees from what I will
call a path of observation” and, furthermore: “the medium can
be thought of as composed not so much of points as of paths”
(Gibson, 1986 p. 197). If we earlier have seen how what Gibson
calls the medium, in an urban setting is structured by particular
configurations of surfaces into spatial form, we can see how
what Gibson is saying here is that such spatial form, can be
represented by a line, or, potentially, a set of lines.
Gibson develops this idea in the context of animal orientation,
which he grounds in what he calls the theory of reversible
occlusion. He describes this in great detail, which proves very
supportive for our attempt to link his ideas to space syntax
representations, such as the axial map:
“An alley in a maze, a room in a house, a street in a town and a
valley in a countryside each constitutes a place, and a place often
constitutes a vista, a semienclosure, a set of unhidden surfaces. A
vista is what is seen from here, with the proviso that ‘here’ is not a
point but an extended region. Vistas are serially connected since
at the end of an alley the next alley open up [. .. ]. To go from one
place to another involves the opening up of the vista ahead and
closing in of the vista behind [. . . ] When the vistas have been put
in order by exploratory locomotion, the invariant structure of the
house, the town, or the whole habitat will be apprehended. [. .. ] It
is not so much having a bird’s-eye view of the terrain as it is being
everywhere at once”. (Gibson, 1986 p. 198).
It is this perception under movement and the sense of the
environment it generates that he means explains the capability
of orientation: “To the extent that one has moved from place to
place, from vista to vista, one can stand still in one place and see
where one is, which means where one is relative to where one
might be” (Gibson, 1986 p. 200). Since what we do, according
to Gibson’s argument, is to continuously scan the environment
rather than take snapshots of it, we are in the end able to generate
a, more or less, shared perception of the world.
Upon closer examination, the axial map turns out to be
something that comes very close to Gibson’s description above
(Figure 2); a network representation of spatial form from
the point of view of what we may call a cognitive subject,
that is, a perceiving human being moving through space.
This is almost an identical description to the one we find
when Gibson attempts to illustrate his theory of reversible
occlusion (Figure 4) (Gibson, 1986, p. 199). In the figure, we
see how the “perceptual spatial unit” continuously changes
as the observer moves through space (the medium), due to
the physical structure of built form (the substance), that is,
particular configurations of built form (surfaces) come into
and goes out of sight for the observer, creating a continuous
set of vistas. This captures Gibson’s idea that we do not
perceive a sequence of discrete vistas when moving through the
environment, but rather a spatial continuum where large parts
of the environment typically remain invariable so that what we
develop is a conception of the environment as perceived from
everywhere.
Now, what we find in the axial map is not a representation
of such a spatial continuum but the least amount of “perceptual
spatial units” that cover the area we want to represent (Figure 2).
These units are represented as lines distinctly crossing each
other as to both connect to each other as a form of continuous
path and to not leave any space possible to access and perceive
outside the representation. The axial map thus constitutes a
kind of representation, of great economy, of what an urban
FIGURE 4 | The opening up of a vista at an occluding edge, as seen from
above (After Gibson, 1986).
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Marcus Urban Models Based on Affordances
environment affords the visibility and accessibility of a generic
human. The representation of this continuous medium in the
form of the least possible amount of “spatial units” of course
represents a reduction of reality, typical for any modeling, but
the gain is that the continuous medium of space, which is highly
difficult to analyse as such, is transformed into a distinct set of
elements possible to represent as a network and also to analyse
as such.
Informed by this discussion we may now return to the
ontological nature of the axial map. We may ask: is it a
representation of the human subject’s conception of urban
space or is it a representation of the environmental object’s
spatial reality. We propose, that it is neither, or rather both,
that is, a representation of urban space that by starting in
the perception of a human moving in such space, captures
what the environment affords its perception. Hence, affordances
are neither part of the environment or of humans, but
rather belong to a human-environment system. The axial
map is then not only a representation of a spatial network
where the individual lines represent different spatial units
tied together at their crossings, but rather a network of
affordances, that is, a series of human-environment relations,
where each line in itself represents such a relation between
humans and the environment; hence the human subject is
written into the axial map to the same degree as the physical
environment.
CONCLUSIONS: LINKING PSYCHOLOGY
TO THE URBAN PLANNING AND DESIGN
OF SUSTAINABLE CITIES
From the discussion above we can draw some important
conclusions. From the point of view of space syntax, we, first, see
that, in contrast to most representations of urban space, the axial
map deals with ecological space in Gibson’s meaning of the word,
rather than physical space. Second, what is represented by the
axial map is not space but the situated affordances that emerge
in the encounter between human abilities and environmental
features. This means, third, that we have a theory about what
it is in these representations that has proven so powerful in
empirical studies of human movement, which in turn could form
the basis for precise empirical tests of this theory. Fourth, this
also opens for the possibility that developments of the axial map,
such as the segment map or continuity line maps, also can be
scrutinized and tested as representations of human affordances,
where they may be found as improvements of the axial map in
this regard.
From the point of view of psychology, we may conclude, first,
that space syntax, and especially the axial map, offers a unique
link between psychological theory and urban modeling, which in
turn means a link between psychology and the practices in urban
planning and design. Second, we see how space syntax can be
useful both in relation to behaviorist and cognitive approaches in
psychology to increased sustainable behavior. On the one hand,
we have seen how it has proven successful in capturing, what we
may call, the behavioral substratum for sustainable behavior in
a more direct sense, in the form of movement patterns and the
distribution of co-presences in urban space. But also, on the other
hand, how these situations of co-presence create the foundations
for specific design of human encounter with urban green, where
particular cognitive experiences relating to values, beliefs, and
norms can be generated.
Hence, we see a highly interesting link between a field
concerned with understanding the relation between humans and
their environment and a field that generate knowledge about how
to intervene and change urban environments, at a time when
we urgently need to redirect our cities into more sustainable
trajectories.
AUTHOR CONTRIBUTIONS
The author confirms being the sole contributor of this work and
approved it for publication.
ACKNOWLEDGMENTS
This article is a reworking and extension of a paper published
in the Proceedings of the 10th International Space Syntax
Symposium at UCL, London, UK, in 2015. The author is most
grateful for the kind permission to publish it here.
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Conflict of Interest Statement: The author declares that the research was
conducted in the absence of any commercial or financial relationships that could
be construed as a potential conflict of interest.
Copyright © 2018 Marcus. This is an open-access article distributed under
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