Category: Research Lines (Page 1 of 2)

“Complex causal structures of neighbourhood change” is published!

One key way that evolutionary processes occur is via feedback loops. A classic way to model such feedback loops is in functional terms. Arthur Stinchcombe articulated the elemental structure of functional explanations in his 1968 book, Constructing Social Theories. In our recently published article, “Complex causal structures of neighbourhood change,” we try to revive this model and demonstrate its value for studying the evolution of cities.

The above figures shows Stinchcombe’s model on the left, and our reformulation of the model for neighbourhood evolution. It codified the causal structure of a complete functional explanation in terms of four core elements:

  1. The consequence that tends to be maintained, which also functions indirectly as a cause of the behaviour or social arrangement to be explained. This is H, the “Homeostatic” variable. Though H may tend to be stable empirically, its stability is maintained against pressures to change it, such as in the case of body temperature.
  2. The social arrangement or behaviour that impacts H, the explanandum. This is S, the “Structure.” In a functional model, Structures tend to maintain Homeostasis. For example, sweat glands tend to maintain body temperature.
  3. Tensions that tend to upset Homeostasis, unless Structures maintain it. This is T, the “tension” variable. If physical activity or air temperature did not alter body temperature, there would likely be no structure to counteract the tensions they create.
  4. Processes that reinforce or select for the S’s (structures) that maintain H (homeostasis). When H is threatened or pressured, these forces increase the activity of S when T (tensions) are higher and decrease when H is maintained. For example, sweat glands generate more sweat (S) when body temperature (H) is not maintained at normal levels due to a certain phenomenon (T). Since this structure helps to maintain H in equilibrium, it will tend to be selected or reinforced.

Stinchcombe’s diagram may be intuitively mapped onto familiar neighbourhood dynamics. For example, we may treat as Homeostatic (H) variables neighbourhood character, style, or scene (such as distinctive shops, restaurants, venues, or groups), Tension (T) variables as pressures to change that character (from, for example, new groups with divergent tastes), and Structure (S) variables as activities that maintain that character (such as Business Improvement Association sponsored festivals, political advocacy, or increased participation in venues and activities distinctive to that scene).

Based on this simple representation, we formulate an initial set of propositions regarding the presence and strength of 1) a functional relationship and 2) a homeostatic response, which can be seen in the paper in more detail.

The key value of such models from the point of considering urban evolution is that treat both persistence and change as a dynamic process. Urban forms of life are retained when there exist structures that preserve them when new challenges. If such structures respond effectively to tensions, there is a tendency for them to be selected and reinforced over time, generating both a pattern of structural retention and possible evolutionary histories of such structures. This idea is scarred further in Part III of “Towards a Model of Urban Evolution,” in our discussion of “retention hypotheses.”

Using data drawn from, we find considerable evidence that the sort of functional process envisaged in the model is a common feature of urban evolution. And in the process we develop novel methods for using data from Yelp and similar sources for such analyses.

We see great potential for using these models and methods for characterizing neighbourhoods in new ways. In contrast to the typical approach, which does so primarily by their demographics or built form, our proposed functionalist approach would identify neighbourhoods with more or less latent potential to resist tensions. In this way, neighbourhoods that look otherwise similar could be shown to have very different probabilities of maintaining their identity over time, thereby allowing planners and policymakers to take these latent functional capacities into account.

While incorporating novel data sources and methods would, to some extent, be challenging, doing so would be in line with parallel proposals. Indeed, local jurisdictions routinely use big data in multiple ways: traffic demand management (using GPS and sensor data), land use (using remotely sensed data), public health (COVID sewage testing), commercial health (using payments data), and more. Our methods could be used in a similar way to monitor tendencies toward neighbourhood change.

From the point of view of social science research more generally, perhaps the biggest result of our study is the possibility of reviving interest in functional explanation. While functional explanation has been characterized as “what any science does,” it has largely fallen out of favour in social science. We review common criticisms, and show that they do not apply to a properly specific functional model of the sort we propose.

At the same time, we find considerable evidence that functionalist motifs are commonplace in neighborhood change research. Researchers typically appeal to functionalist motifs when they discuss for example the capacity of local groups to push back against tensions or challenges as a key mechanism producing continuity or change.  However, we found no examples in the neighbourhood change literature where an author who utilized a functionalist motif articulated the motif in an explanatory model that would render it testable. Instead, much neighbourhood change research remains largely descriptive, mapping types and directions of change across a range of variables.

We hope one result of our study is to illustrate a path for remedying this situation, which in turn would help to more formally incorporate evolutionary thinking into urban research.

Toronto Urban Evolution Model Paper Series Published!

A central theoretical goal of the Urban Genome Project has been to articulate a model of urban evolution. We develop the model in four papers, recently published together in Urban Science. The paper series is called “Towards a Model of Urban Evolution,” because its central task is to elaborate a rich yet rigorous formal language capable of formulating propositions about the evolution of cities.

Paper I is “Context.” It proceeds in four major sections. First, we review prior adumbrations of an evolutionary model in urban theory, noting their potential and their limitations. Examples include Chicago School Ecology, stage theories, and theories of cities as complex adaptive systems. Second, we turn to the general sociocultural evolution literature to draw inspiration for a fresh and more complete application of evolutionary theory to the study of urban life. Third, building upon this background, we outline the main elements of our proposed model, with special attention to elaborating the value of its key conceptual innovation, the “formeme”. A formeme is a specific encoding of urban space as a combination of physical features and the groups and activities toward which they are oriented.

In turn we discuss the value of the model, highlighting its extension of the basic inferential logic of population genetics and evolutionary ecology into the urban domain, including the goal of replacing essentialist with distributional thinking, group and development thinking with tree and network ideas. Last, we conclude with a discussion of what types of research commitments the overall approach does or does not imply. Among other things, we note that an evolutionary model of the sort we develop is neither reductive nor deterministic, nor is it necessarily progressivist or teleological. We conclude by suggesting that an evolutionary approach suggests embracing new metaphors for the role of the planner: the planner less as an engineer pulling the levers of a well-tuned machine and more as a gardener in a forest, seeking to cultivate a rich ecosystem while remaining sensitive to processes unfolding through their own dynamics.

Type of DependenceSummaryExample
Principles Related to Form Features
ScopeFormemes with wider niches will tend to attract more resources. Formemes with wider niche width will have a relativity higher probability of survival when the environment is changing, specialized forms will be favored under stable conditionsMcDonalds has a wider niche width than a vegan, organic hamburger stand.McDonalds is more likely to survive a 30% increase in the local minimum wage or a pandemic than the local hamburger stand.
ContentThe viability of a formeme will be influenced by its proximity to groups with a preference for or against the substantive content of its activities or the group affiliation it affirms.Ethnic shops will tend to proliferate in areas where members of that ethnicity reside; satanic book stores will have low survival rates nearby Evangelical Christian populations.
Distance Propagation of a formeme depends on how physically close it is to other iterations of the same formeme.The franchise of a successful operation will be more viable at some ideal physical distance from the original 
Principles related to environmental features
DensityPropagation of a formeme depends on density of competitors in the environmentNeopolitan pizza thrives when there is a glut of pizza restaurants
FrequencyPropagation of a formeme depends on the size of the formeme’s populationThe 28,000th Starbucks location propagates at a different rate and in different places than the first.
Principles Governing the Evolution of Urban Form

Paper II elaborates the formal model. It defines the Signature of an urban space, comprised of the information encoded in that space. This information consists of: an urban genome, which captures ideas regarding the groups (i.e., users) and activities (i.e., uses) to which a space’s physical forms are oriented; ideas among human actors regarding who (users) and how (uses) to utilize the space and its forms; and the signals that are communicated within and among urban spaces. Central to the model is the notion of the formeme, which provides the building blocks for a Signature. Formemes are units of urban information regarding physical forms, groups, and activities, which may be encoded in physical artifacts, signals, or human actors, and circulate among them. We then show how various metrics can define an urban area based on its Signature, and that these metrics can be used to measure similarity of urban spaces. The Signature, and its underlying formemes capture the sources of variations in urban evolution.

Paper III, “Rules of Evolution,” illustrates how to use the model to formulate propositions about urban evolution. It highlights (1) sources of variations; (2) principles of selection; and (3) mechanisms of retention. More specifically, regarding (1) it defines local and environmental sources of variation and identifies some of their generative processes, such as recombination, migration, mutation, extinction, and transcription errors. Regarding (2), it outlines a series of selection processes as part of an evolutionary ecology of urban forms, including density dependence, scope dependence, distance dependence, content dependence, and frequency dependence. Regarding (3), it characterizes retention as a combination of absorption and restriction of novel variants, defines mechanisms by which these can occur, including longevity, fidelity, and fecundity, and specifies how these processes issue in trajectories define by properties such as stability, pace, convergence, and divergence.

Paper IV, “Evolutionary (Formetic) Distance” provides an application of the model, using data from It demonstrates how the Toronto Urban Evolution Model (TUEM) can be used to encode city data, illuminate key features, showing how formetic distance can be used to discover how spatial areas change over time, and identify similar spatial areas within and between cities. In this application, each Yelp review can be interpreted as a formeme where the category of the business is a form, the reviewer is a group, and the review is an activity. Yelp data from neighbourhoods in both Toronto and Montreal are encoded in this way. A method for aggregating reviewers into groups with multiple members is introduced. Specifically, we use the Apriori algorithm to aggregate reviewers by the types of venues they visit. Performing group aggregation using a level-wise search, this algorithm abstracts groups based on the forms they conducted reviewing activities for. Building on this basis, longitudinal analysis is performed for all Toronto neighbourhoods. Transversal analysis is performed between neighbourhoods within Toronto and between Toronto and Montreal. Similar neighbourhoods are identified validating formetic distance.

Dynamic models of urban segregation



Thomas Schelling’s classic paper is a key reference point for agent-based models of segregation.  It is often taken as providing fundamental insight into the micro-processes that produce the segregated macro-structures that characterize urban settlement patterns.   In this research tradition, however, urban form plays a very limited role, despite the fact that Schelling himself introduced his model by reference to venues (such as churches) and spatial areas (such as neighbourhoods).   Form is generally reduced to an agent’s capacity to ‘see’ nearby grid-cells of the simulation world: an agent’s neighbourhood is its Moore neighbourhood.

In this research, we argue that an analytically meaningful simulation of neighbourhood formation – or more specifically of integration and segregation dynamics – must acknowledge the role of built form. We introduce a model of physical venues into the classic Schelling model in order to reconsider the simulation’s dynamics as influenced by both the spaces where agents live and the spaces of their activities. Venues structure the urban environment because i) they are foci of interaction and ii) their number and physical distribution constrains agents’ behaviour.  Articulating and observing the consequences of some simple rules for the interaction between agents and venues, we are able to generate characteristic combinations of integration and segregation that have distinctive urban features lacking in typical Schelling-type models.  Moreover, whereas in Schelling-inspired formulations, once a pattern of segregation congeals it is nearly impossible to change, we show that under some circumstances shifting the location of venues may break or redefine underlying patterns to some degree.

In a series of four case studies of increasing sophistication, we observe novel combinations of integration and segregation, brought about by the interaction between agents and venues. In our first study (1), we investigate different spatial configurations of venues from simple geometric distributions to a core and periphery model. Findings highlight the more realistic settlement patterns emerging from the interplay of a planned configuration of venues and the self-organizing behaviour of agents. In our second study (2), we consider variations in a venue’s exclusivity – the extent to which venues of a given group are open to admitting members of other groups. We discuss the parameters under which a range of outcomes result, from integration made possible by adjacent and exclusive venues, to ‘co-opting’ that can be caused by highly inclusive venues. In the third study (3), we build on prior experiments in the literature that have examined unequal populations, and demonstrate how majority/minority dynamics are affected by the presence of physical venues. Finally (4), after noting the high stability of segregated outcomes in Schelling-style simulations, we apply our venue model across a range of parameters in order to evaluate conditions under which settled, segregated neighbourhood patterns become disrupted.

In addition to their particular substantive points, a persistent interest of these studies is whether – and under what parameter ranges – access to group-specific venues allows individual agents to be comfortable remaining in a more diverse neighbourhood vs. these same venues becoming attractors that reinforce Schelling dynamics of segregation. In the process of introducing the case studies, we also describe and deploy a series of methodological innovations. For example, we begin each study with a visualization of the variety of simulation outcomes across value ranges of two input parameters (for example “intolerance threshold” vs. “max travel distance”). These representations, which we refer to throughout as parameter spaces of the simulations, organize the discussions of our findings and allow us to emphasize significant steps or thresholds, where small changes in the input parameters yield large changes in the results (Schelling’s classic example of which is the intolerance threshold around 1/3rd). Where necessary, we also introduce specific techniques of visualization and analysis to effectively characterize the movements of agents and the resulting patterns of clustering in relation to the built form of the simulations.

A working draft of the paper is available here.


The urban ecology of popular music



Cities are breeding grounds of distinct modes of cultural activity.  In this study, we examine how popular musicians define themselves differently depending on their location.  In particular, we examine the relationship between bands’ degree of conventionality and unconventionality and their popularity.  We show that this relationship in general exhibits a non-linear, inverted U pattern: extremely conventional bands are relatively unpopular, somewhat unconventional bands show more popularity, while the most unusual bands are not very popular. 

However, this general pattern shifts, across musical genres and geography.   Some cities show greater receptivity to unconventionality, with more unconventional bands achieving greater popularity, while in others more conventional bands tend to thrive.  We examine several features of the urban environment that might explain these variations. We do so using a large database of nearly 3 million band profiles from, circa 2007.  

An interactive tool for exploring these relationships can be accessed here

Political order of the city



While cities as a whole can be viewed as distinct ecological environments, they also have their own internal ecological order made up of a variety of local niches.  These niches are not independent of one another, but interact to produce and reproduce a characteristic order that persists through time, even as individuals move about and change.  In this study, we examine and develop the notion of the political order of the city as constituting a crucial aspect of urban ecology, using Toronto as a case study but also exploring similar relations in London, UK.  

To do so, we combine insights from urban studies, political science, and geography to examine the spatial articulation of urban politics. We deliberately speak of a “political order” rather than a “political structure” to emphasize relational patterns while allowing for change in, and selective activation of, their ordering principles. We develop a framework for examining urban politics that features three core concepts: order, cleavage, and activation. Regarding order, we suggest that neighborhoods exhibit political patterns that tend to persist across elections. These patterns embody spatially-entrenched cleavages, which inform neighborhoods’ relationships to the city as a polity, as well as other neighborhoods. We suggest that cleavages become politically salient must be activated through mechanisms such as political campaigning, and that activated cleavages may in turn alter the views and experiences of residents in city neighborhoods.

We find that Toronto’s political order revolves around two major cleavages.  One divides the city’s progressive core from its more conservative suburban areas, and turns primarily on features of urban form and transit patterns, such as housing type and commuting method.  The other is primarily intra-suburban, and divides the city’s traditionally upper-status Establishment areas from its more marginalized communities; this cleavage turns on factors such as income, religion, and occupation.  

Having described the nature of Toronto’s political order, we then examine how it relates to individuals’ actions and attitudes, showing that individual Torontonians’ voting behavior is strongly connected to the particular political zone of the city in which they reside, and that individuals’ confidence in a range of social institutions shifts depending upon the political fortunes of their neighbourhoods. These analyses show that the meso-level ecological patterns we find are not readily reducible to the demographic characteristics of individuals; rather, the political order is a reality with significance in individuals’ lives, a social fact to which people respond in various ways.

Some interactive maps of Toronto based on this research have been published in the Toronto Star

Darwin’s Dangerous Idea of a City


This project is an effort to extend and adapt basic evolutionary concepts to the study of cities.  It starts from the proposition that urbanites are a city’s way of making another city.  Cities encode information about how to make new versions of themselves.  This information contains implicit instructions for the types of uses and users that would recreate the city, or more specifically the various features and forms that comprise it.  But this code cannot run itself, it requires facilitating conditions that can process it: urbanites.  In running the urban script, urban dwellers are recruited into making tomorrow’s city resemble today’s.  As this takes place in a shifting, uncertain, competitive, and complex environment, this is far from a static or deterministic process. The genetic code of cities is constantly evolving through mutations, selective pressures of various forms, differential replication, and related processes.

Taking this statement seriously orients the Urban Genome Project.  A first and major theoretical challenge is to transform this intuition into a tractable model that can inform research.  The goal is to fashion a structured yet flexible vocabulary for formulating and exploring hypotheses about urban genetics.  This model is not created anew from whole cloth.  Rather, it joins elements and ideas from diverse fields of urban and related research into a synthetic framework.  Nor does it seek to determine a priori all relevant variables and how they should be stratified. Yet it does aim to provide a vocabulary for evaluating and comparing potential variables, and guiding questions about how these variables might fit together. 

We pursue this theoretical project along a number of related fronts.  A first step is to articulate a formal definition of the urban genome and the interconnected elements that sustain and change it.   These all cohere in what we term the “Signature.”  

Sig(c, t, F, L, S, E, w)

The Signature encodes, for some spatial area c, at time point or interval t, the physical form, plus information about its intended or implied uses or activities, and intended or implied users or groups (F).  Information about F is transmitted via some signal (S), and reproduced by agents through L which specifies the actual activities performed by actual groups of people, plus the resources available to the groups to perform activities. All of this takes place within a broader macro-environment (E). Finally, w represents a “world” in which the signature exists. In most cases, we will omit this parameter, but when we need to compare alternative signatures for the same space c and time t, w will be used to distinguish them (i.e., alternative worlds).

A second step builds out this model to show how it can be used to articulate processes of recoding.  Recoding occurs when the urban genome (F in the Signature) is changed.  We elaborate several ways that this can happen, for instance through changes in the Environment (Environmentally Induced Recoding), in the activity patterns and identities of agents (L induced recoding), or in the nature and reach of Signals that convey information about the genome (Signal Induced Recoding).

A third step moves from recoding to replication, and introduces the concept of the formeme.  Formemes are urban versions of memes — small bits of urban form that replicate, such as the cul-de-sac, the bohemian neighbourhood, streetscape design, or public art.  Adapting concepts from population genetics, we develop models for the study of population formetics, which examine changes in the formetic diversity of urban populations.  Key processes that shift formetic diversity include migration, mutation, and selection.  As formemes spread and adapt, they form lineages and are subject to differential survival rates, generating the basis for evolving urban species.

Last we develop concepts for studying more complex evolutionary processes, in which multiple genomes, signatures, and formemes combine into larger complexes that in turn create distinct ecologies.  Examples of such processes include seeding, scaling, and niche construction.  

An evolutionary ecology of urban form



One crucial way that urban forms emerge, transform, and spread is through defining them as spaces geared for specific activities.  This imposes costs on using them for different activities, making them more likely to persist, but also perhaps decreasing flexibility.  This project develops a case study of this dimension of urban formetics, studying the spread of certified Neapolitan Pizza establishments across and within cities. By developing a case, we hope to contribute to a more refined understanding of key concepts in the UGP and illustrate how they might be studied.  Key questions include:

  1. What kind of urban environment did this pizza style emerge out of?
  2. What kind of urban environments, did this pizza style spread to?
  3. Are there regularities in the spatial diffusion of Neopolitan pizza over time?

To develop and pursue these propositions, we adapt key ideas from evolutionary ecology, such as density dependence and niche width. 

For example, we hypothesize that uncertified pizza is likely to proliferate where density of pizza and similar establishments is low; by contrast, certified pizza is likely to emerge where the pizza carrying capacity is near its threshold, and success depends upon quality indicators.  We also hypothesize that other mechanisms are at work.   For instance, content bias: Neopolitan pizza should initially appear in spatially and socially proximate areas, i.e. it should appear both nearby its “home” and in areas with high proportions of Italian immigrants.  Frequency bias: as it spreads, others copy it, thereby increasing its niche width to more socially diverse environments.  

Public Art Policies as vehicles by which urban forms spread



Formemes are reproducible bits of urban form.  Though they circulate through various mechanisms, urban policies are key conduits through which forms are transmitted.  This study investigates how urban forms spread through an examination of public art policies.  Using a corpus of hundreds of policy documents from over 25 cities covering over forty years we pursue three major research questions:

1) What are the main ways that these documents speak about Public Art?

2) When and where these ways are taken up? 

3) What are the determinants that shape the taking-up of any of these possibilities? 

Patchwork metropolis


San Francisco's Urban Form


Urban Studies has periodically been concerned with establishing dominant models for urban form, among them: “The Concentric Ring”, the “Multiple-Nuclei” the “Hole in the Donut” and more recently the “Great Inversion”.   This project hopes to contribute to this tradition by bringing modern mapping and image processing techniques to the understanding of models of urban form. Does the pattern of streets and residents conform to a or a few discrete models? As cities develop does their form converge on some higher order model? 

The patchwork metropolis: The morphology of the divided postindustrial city

The scope of urban scale


Scaling is a basic process that characterizes many forms of life.  It refers to the fact that key features of entities strongly depend upon their size, and that in many respects larger versions of life-forms are scaled up versions of smaller ones.  For example, while elephants and mice have very different heart rates, their hearts beat about the same number of times over the course of a lifetime.  Likewise, many features of cities — such as the number of gas stations or patents — can be reliably predicted simply based upon their population size.  According to this view,  developed by Geoffrey West, Luis Bettencourt, and colleagues, larger urban forms are scaled up versions of smaller ones.

This parallel between basic features of organic and urban life has spawned a robust yet recent research tradition devoted to the study of urban scaling laws.  Central to this research is the observation that entities may scale superlinearly, sublinearly, and linearly, often referred to as “scaling regimes.” This means that a feature may increase faster (super), slower (sub), or at the same pace of the city size.  Sub-linear scaling represents economies of scale, whereas super-linear scaling is associated with increasing returns to interaction (which may result in higher crime rates or greater innovation).  Some observers see scaling in terms of innovation cycles and the evolutionary theory of urban systems – superlinear regimes characterize innovative sectors, whereas sublinear regimes result from the diffusion of innovations throughout the system. 

Our research problematizes a key assumption of this tradition: that scaling regimes depend upon the definition of the city in question, in particular its geographic borders.  Rather than search for the ‘true’ definition of the city’s boundaries, however, we instead suggest viewing cities as operating simultaneously at multiple scopes and scales.  For example, New York’s financial services industry on Wall Street may have a much wider scope than a gas station on the same street.

Building on this insight, we develop a series of techniques to identify and understand the scope at which various local features scale.  In particular, we deploy a search algorithm that finds for any feature (e.g. business types) the geographic area in which it reliably scales with population.  These scopes vary widely.  Second, we use these measures of scope to propose a new way to differentiate cities, in terms of size and variety of the scope of experience they offer.  In some cities we exist in large and diverse scopes, in others most scopes are small and similar.  Third, we examine how scope varies across the urban system, and fourth how it has evolved over time.  Overall, this research develops a more complex notion of cities as complex systems of features operating and interacting at many different scales. 

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