Category: Blog Entry (Page 1 of 3)

“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.

Residential Micro-Segregation via Street Barriers in Lima, Peru

By Fernando Calderon Figueroa

Description of the Study

This study addresses the relationship between residential micro-segregation, in the form of built barriers to urban mobility, and social capital. Most of the scholarship on residential segregation posits the neighbourhood as its most relevant scale of analysis, while discussing built barriers as expressions of pre-existing social boundaries and as the result of higher-status groups’ attempts to seclude themselves from lower ones (Caldeira 2000; Garrido 2019; Massey and Denton 1993). A recent thread of studies has shown the importance of the street level for segregation patterns by bringing attention to the built environment (Grannis 1998; Grigoryeva and Ruef 2015; Logan, Graziul, and Frey 2018; Roberto 2018). Following this line of work, I draw on the notion of spatial micro-segregation to describe the patterns of urban fragmentation that result from resident-driven street enclosures within and across neighbourhoods.

I attempt to empirically test two theoretical propositions:

  • Residential micro-segregation is a socio-spatial process that occurs in the more recently developed residential areas of highly unequal cities that cuts across socioeconomic and ethnoracial boundaries.
    • Empirically, this proposition implies that micro-segregation must be pervasive throughout residential neighbourhoods and particularly concentrated among the most recently developed ones. There should be no correlation between the density of street barriers (e.g., gates, fences) and the socioeconomic or ethnoracial heterogeneity within and across neighbourhoods.
  • Residential micro-segregation negatively impacts the development of social capital and sentiments of community. Barriers to mobility express a form of social closure defined by location that interacts with the existing sociodemographic and ethnoracial composition of the neighbourhood.
    • Empirically, this proposition suggests that measures of social capital (e.g., interpersonal trust) should have decreased in the past few years in areas of the city with higher concentrations of street barriers.

To test these hypotheses, I use the case of Lima, Peru. I draw on the OpenStreetMap project (OSM) to identify the thousands of street-level barriers to mobility built in the city since the late 1990s. OSM is an open access platform, which allows the data to remain public beyond the scope of this study. While a fraction of street barriers has been reported, I am completing the data using georeferenced photographs posted on Mapillary and directly collecting images using an unmanned aerial vehicle (UAV or drone). The sociodemographic and ethnoracial composition comes from the block-level sociodemographic data published by the Peruvian National Institute on Statistics and Informatics (INEI) for the most recent census years (2007 and 2017). To assess social capital changes over time, I use an annual survey (N≈1,200 per year) on community issues conducted since 2010 called Lima Cómo Vamos.

This paper aims to expand our current knowledge about segregation patterns and their implications for social capital in highly unequal cities such as those in Latin America and throughout the Global South. I expect to complete a draft of the article by the end of 2022.

Preview of Spatial Analysis

Here is a preview of the street barrier data collected so far using OSM. The map shows the barriers, by category, in Villa El Salvador, a district in the south of Lima.


Caldeira, Teresa P. R. 2000. City of Walls: Crime, Segregation, and Citizenship in São Paulo. University of California Press.

Garrido, Marco. 2019. The Patchwork City: Class, Space, and Politics in Metro Manila. University of Chicago Press.

Grannis, Rick. 1998. “The Importance of Trivial Streets: Residential Streets and Residential Segregation.” American Journal of Sociology 103(6):1530–64.

Grigoryeva, Angelina, and Martin Ruef. 2015. “The Historical Demography of Racial Segregation.” American Sociological Review 80(4):814–42. doi: 10.1177/0003122415589170.

Logan, John R., Chris Graziul, and Nathan Frey. 2018. “Neighborhood Formation in St. Louis, 1930.” Environment and Planning B: Urban Analytics and City Science 45(6):1157–74. doi: 10.1177/2399808318801958.

Massey, Douglas S., and Nancy A. Denton. 1993. American Apartheid: Segregation and the Making of the Underclass. Cambridge: Harvard University Press.

Roberto, Elizabeth. 2018. “The Spatial Proximity and Connectivity Method for Measuring and Analyzing Residential Segregation.” Sociological Methodology 48(1):182–224. doi: 10.1177/0081175018796871.

New paper published! The Dilemmas of Spatializing Social Issues

Illustration by Fernando A. Calderón-Figueroa

Urban Genome Project Members Fernando A. Calderón-Figueroa, Daniel Silver, and Olimpia Bidian’s paper discussing Toronto’s Priority Area Program (2006–2013) has just been published in Socius: Sociological Research for a Dynamic World. Here’s Fernando’s summary:

Among the multiple ways to subdivide a city, neighbourhoods are probably the most familiar to our everyday experience. It is not surprising that neighbourhoods have been at the centre of revitalization efforts for almost a century. Yet, the early 2000s marked a transition towards systematic efforts to define neighbourhoods and their boundaries and identify the most disadvantaged among them. We call this process the spatialization of social issues, which was largely facilitated by the proliferation of Geographic Information Systems (GIS) technology in both academic and policy circles. More importantly, planning decisions that emerged from this trend affected neighbourhoods’ trajectories over time beyond policymakers’ original intentions.

Our paper explores the unwanted consequences of spatializing social issues in three steps. First, we examine whether designating entire neighbourhoods for social policy may affect their desirability as expressed in changes in rent and housing prices and in new building permits. Second, we assess the extent to which designated neighbourhoods may leave out areas “in need” that fall outside their boundaries while including better-off families within them. Third, we analyze evidence on whether this spatially-targeted policies may expand the stigma associated with certain places—e.g., a “dangerous” intersection or a “poor” housing complex—to all the designated neighbourhoods and the people within them. We draw on difference-in-difference models and income distribution analysis for first two parts, and on a qualitative assessment of newspaper articles and policy documents for the third one.

We make a twofold intervention in the existing literature on place-based policies. First, we bring together two social policy debates that share the common goal of attempting to improve the quality of life of those in areas of concentrated disadvantage. The “targeted” versus “universal” debate, heir to the 1970s welfare state scholarship, addresses the effectiveness and drawbacks of each of these approaches. The second is the “individual” versus “place” debate, in which researchers assess whether urban revitalization efforts should focus on individuals or entire places (e.g., “enterprise zones”). We bring together these traditions by treating each approach—targeted, universal, individual, and place—as dimensions in a two-by-two table. This intervention allows us to identify the potential negative externalities of neighbourhoods as policy targets (the targeted-place approach) while uncovering the potential of less-explored possibilities beyond spatial designations (the universal-place approach). Our second intervention is to bring to the fore a sociological conception of the neighbourhood that highlights its singularities as a scale of policy intervention. We suggest that neighbourhoods are interwoven in the urban landscape—thus, treating them as isolated entities poses significant challenges—and that their reputations matter for people’s self-conceptions and decision-making processes.

The study examines these ideas through the case of the Toronto Strong Neighbourhoods Strategy as it was implemented between 2006 and 2011. The program established 13 “priority areas for investment” and aimed to channel federal, provincial, and municipal resources into underserved communities to improve their social infrastructure. This was a response to the increasing poverty and crime rates in Toronto’s inner-suburban neighbourhoods. Previous research has found mixed evidence of the program’s effectiveness. However, we focus on assessing its unintended consequences, particularly regarding the lasting impact of the “priority neighbourhood” label as a shorthand for the target areas even after the program was relaunched in 2011. We find that, compared to otherwise similar and nearby places, those that received the “priority” designated had substantially lower growth in home prices, building permits, and rents.




Figure 2. Graphs (a) and (b) show trajectories comparing undesignated (red) and designated (light blue) DA paths on average monthly rent (left), average dwelling value (centre), and the cumulative sum of building permits (right) before (a) and after (b) matching. In graph (a), the markedly different trajectories respond to comparing the priority areas with the rest of the city. Graph (b) shows narrower trajectories albeit the growing gap between undesignated and designated areas across the three outcomes remains. Finally, graph (c) splits the priority areas between neighbourhoods designated by the CSP (green) and those included by the SNTF (light blue). The plots in graph (c) show that the gap between undesignated and designated DA paths grows wider over time for the CSP priority areas. Each outcome (column) has a different scale. 

The paper does not aim to entirely dismiss place-based policies but to expand how we think about them. Current location-based technology allows better ways to identify neighbourhoods and people’s needs for social infrastructure based on mobility and consumption patterns, street connectivity, among other measures, rather than relying on imposed official boundaries. Targeted policies may be combined with more universal approaches that reduce spatial inequalities while using resources efficiently. Our goal is to bring back sociological view of neighbourhoods as complex and interdependent foci of social life rather than isolated policy targets.

Listen to lead author Fernando A. Calderón-Figueroa discuss this paper by streaming the video below.

New Paper: “The Space of Ideas: Public Art Policies and the Concept of Urban Model Spaces”

an illustration of cloud gate (bean) in chicago

Noga Keidar and Dan Silver are  excited to announce the publication of their paper in The Journal of Urban Affairs. As a PhD candidate in the Department of Sociology at the University of Toronto Dr. Keidar was inspired to follow public art policies in order to examine the evolution of policy ideas and explain the mechanisms behind their mutations: “Our exploration started in 2016 as part of a research group of scholars from the U of T and OCAD U that worked to improve Toronto’s Percent for Art mechanism. We began collecting policy materials from cities comparable to Toronto to get ideas about how things could be done differently. We were surprised by the richness of policy materials cities produced, and more importantly by the great variance of values, goals and procedural arrangements that developed from this relatively basic policy tool. We wanted to systematically examine how the concept developed over time, across physical space and institutional settings, and to explain why cities used it differently. A key challenge was to develop a method and a theoretical framework to compare many cities. This challenge urged us to develop the Urban Model Space that could be applied in a textual analysis for any other popular policy model. 

Here is a short synopsis of the paper:

One of the central components of the theory of urban evolution concerns the circulation of urban ideas. Ideas about how to physically organize space, what to do there, and who should be there – forms, activities, and groups – carry from place to place what we term “formemes” in “Towards a Model of Urban Evolution.”

Our forthcoming article, “The Space of Ideas,” elaborates a novel approach to studying the role of urban ideas in urban evolution. Using a large corpus of public art policy documents from 1959-2020, we use computational text analysis to uncover the latent structure of the Anglosphere public art discourse and how it evolves along three key dimensions: temporality, scale, and position. We find six recurrent themes predominate in what we term the public art “Urban Model Space.” These themes include topics we describe under headings such as “pedestrianism,” “equitable access,” “creative industries,” “place-based identity,” “creative opportunities,” and “heritage.” Our analysis shows that the adoption of these themes is shaped by factors such as when a city initiates a public art program (temporality), the region or state in which it is located (scale), and its position in the global urban hierarchy or internal agency leading its public art initiatives (position). While the analysis offers important insight into the domain of public art, it also serves as a model for incorporating textual representations of ideas into urban evolutionary research.

To read the full article, click here.

Our study builds upon a dynamic and robust research tradition into Urban Policy Mobility. During the last two decades, this research stream has been documenting an extensive ‘flow’ of “urban models”, like Business Improvement Districts, Arts and Cultural policy, Climate Solutions and Insurgent Practices of slums and shack dwellers (McCann and Ward, 2010; Cociña et al., 2019; Wood, 2016). While these urban models are often described as ‘one-size-fits-all’ formulas shaped by homogenizing forces of globalization, they also generate replications and mutations that may be more ‘progressive’ or ‘conservative’, ‘market-led’ or ‘community-oriented’, depending on the interactions with a particular city (McCann, 2011; Jacobs, 2012). The attempt to assess the local formulation of a model is often tackled through a case study method that follows the local translation and compare it with few other translations. However, to fully understand policy replications and mutations, we must examine various translations of the ‘same’ model and locate them as part of the broader structure that explains their emergence. Our study proposes a complementary approach to the standard detailed case study – a textual analysis that delineates the Urban Model Space in which the implementation of the model in a specific location is situated alongside others.

To illustrate the approach, we use public art policy and in particular the Percent for Public Art ordinance – a common funding mechanism in the Anglosphere of setting aside a percentage of the city’s capital budget for public art. We sketch the space of the public art policy model using a corpus of public art policy documents from 26 cities with more than one million residents in the Anglosphere, including Australia, Canada, the United Kingdom, and the United States. These documents cover the period from when the ordinance was first applied in Philadelphia in 1959 (Carlin, 2004) until 2020. The corpus consists of four types of documents: public art plans, broader cultural plans with public art sections, guidelines, and open-ended research reports. These documents are used for various practical purposes, like creating a basis of common knowledge, standardizing technical procedures, promoting a policy change, or publicizing the city’s policy models over the world. After identifying the main discourses describing public art with Structural Topic Models (STM), we determine where, when, and why they were adopted with a series of regression analyses. Specifically, we ask: How have public art discourses changed over time? Which scale matters more for which topic? And which types of positions matter for the adoption of each discursive category?”

New City Research Insights Features UGP

The latest edition of the School of Cities City Research Insights features the Urban Genome Project. Below is a selection, you can read the whole piece here.

“A multidisciplinary working group, established under the banner of the
Urban Genome Project (UGP), is renewing connections between the life and physical sciences and the social sciences to decode the DNA of the city. Supported by the School of Cities, co-leads Daniel Silver (Sociology) and Mark Fox (Industrial Engineering and Computer Science) are exploring how the concept of evolution can apply beyond the study of living things to help us better understand our cities and the processes that influence change within them.

Originally inspired by the Human Genome Project, UGP has involved ongoing collaboration among faculty and graduate students from sociology, industrial engineering, computer science, architecture, biology, economic geography, and others at U of T and partner universities.

While the application of evolutionary concepts to cities is not entirely new, the Urban Genome Project is attempting to join them together into a novel general evolutionary model for cities. The model provides a framework for understanding how various city characteristics appear at different rates and in different places, and for understanding how those characteristics may have shared or divergent development patterns across time and space.

An urban evolutionary approach can reveal why and how certain urban characteristics – such as porches, cul-de-sacs or racial segregation – exist within cities, how those characteristics come into being, and why the number of them and how they function changes over time. Using an evolutionary lens can also tell us about how urban neighbourhoods and communities adapt to changes in built form or changing demographics, how our views of places change as the city evolves, and how to introduce policy interventions that are informed by and responsive to what is happening in a given place and time.”

Public-Spiritedness in the Metropolis

What place is there for public spiritedness in the metropolis? Here, public spiritedness is broadly defined as a sense of obligation to others, which is presupposed by a sense of community. This definition considers the humanity of others, even if they are strangers. It suggests that there is a spirit, a personal philosophy, that is rooted in the desire to consider the welfare of not just the self, but of others too. Public spiritedness in this sense is most conducive to desirable outcomes in a society when it is practised by the masses. Otherwise, the incentive to care for others when others do not care for you diminishes. There is no pleasure in being a victim amidst a collective action problem: no one wants to be in an unfair position of supporting a “free-rider”. As such, public-spiritedness is a way of life that is practised by the self, but yields maximal benefit and becomes most compelling when it is practiced by a collective.

The anonymized nature of being in a city makes the practice of public-spiritedness more difficult than in a smaller community—like one typical of a rural area. In a city with millions of people, it becomes more difficult to consider the humanity of others due to the impossibility of meaningfully engaging with a sizeable fraction of a city’s residents. This lack of engagement not merely inhibits one’s ability to consider the humanity of the other when most of the others are unknown. It also inhibits one’s ability to gauge the level of public-spiritedness practiced by others in the city. As such, it may seem that the rational position is to act selfishly without regard for other community members.

Given the desirability of public-spiritedness, what place does it occupy in a city? Surely, there ought to be physical venues in which acts stemming from public-spiritedness can be displayed. Displays of this sort are prime examples of “signals” in the Toronto Urban Evolution Model: they transmit ideas about how to properly organize urban life. Signals can include formal material such as policy documents but they also include the everyday ways in which urbanities communicate to one another the models of urban life they value. Accordingly, some physical venues may signal the practice of selflessness to deter suspicions relating to collective action issues, but also emphasize the goodness of a city’s inhabitants. But the practice of public-spiritedness is also a private one that manifests in situations away from the public eye. To be conscientious of the humanity of the other requires an internalized understanding of how neighbours, no matter how near or how far, are people, too. They may be someone’s mother or someone’s brother. They have basic needs like access to food and water, but also personal needs like dignity and love.

This essay will focus on the porch as physical places for cultivating public- spiritedness and a key site for the evolution of “formemes.” It does not suggest the decline of the porch coincides with the loss of a sense of public-spiritedness, as Richard H. Thomas suggests in his “From Porch to Patio.” This essay is a celebration of the porch as an historically significant space for public gathering, both intentional and accidental.

Porches have evolved over millennia to reflect architectural waves and cultural contexts. Porches predate the bible, in which they may be referred to as “covered ways,” “porticoes” and “colonnades.” The porch, in the biblical context, more closely resembles the agoras (open place of assembly) observed in Greek documents like Plato’s Republic. By this, I mean the porch is a place at which individuals congregate intentionally, rather than on a whim as one might in the case of a neighbor’s porch in the context of a modern American suburb. In Acts 5:12 (Common English Bible), “The apostles performed many signs and wonders among the people. They would come together regularly at Solomon’s Porch.” This porch is not a small enclosure by a home’s entry way. This religious place of prayer and miracle is more fittingly built as a long pillared walkway running the entire eastern side of the Temple’s Outer Court in Jerusalem. As Solomon’s Porch, along with the rest of Herod’s temple, was destroyed by the Romans in A.D. 70, modern-day understanding of porch’s purpose and appearance largely relies on its observations in the Bible.

The porch has lived on as a symbol for congregation vital to the health of communities. TADAMUN Initiative declares “public libraries, community centers, public schools and places of worship […] [as] the “front porches” of civil society” in their declaration for the need of public spaces “accessible to all citizens, regardless of race, age, gender, income, or religion”. Here, the porch is a space not exclusive to any religious population: it is an open and public space to achieve the goods necessary for a community’s standards of a good life (e.g. access to education, social connection, freedom to worship).

Robert Putnam, when referring to social capital in “Bowling Alone,” also mentions the role of the porch in a healthy community. He observes “porch stoops” as places for “the community ‘mothers’ [to serve] as the neighborhood’s eyes and ears”. He admires the Rosteans, the inhabitants of Roseto, a modest village nestled in Eastern Pennsylvania, for their abundant social capital: “By day they congregated on front porches to watch the comings and goings, and by night they gravitated to local social clubs. In the 1960s the researchers began to suspect that social capital (though they didn’t use the term) was the key to Rosetans’ healthy hearts.” In this context, the porch is a necessary venue for companionship and support during the day. In his research on the decline of social capital, Putnam observes the rise of vocational communities amidst the decline of locational communities (like the Rosteans’). In writing, “perhaps we have simply transferred more of our friendships, more of our civic discussions, and more of our community ties from the front porch to the water cooler,” Putnam suggests the function of the porch has been transferred from home-based to work-based spaces.

Like Putnam, Richard H. Thomas identifies the necessity of deliberation among community members and likewise the importance of spaces to host such deliberation. In his “From Porch to Patio,” he laments the fall of the front-facing porch amidst the rise of the private, enclosed back patio. Whereas the sense of community that “often characterized the nineteenth-century village resulted from the forms of social interaction that the porch facilitated,” the “twentieth century man has achieved the sense of privacy in his patio [in exchange for] part of his public nature” (126-127). The back facing patio, irrespective of whether it is enclosed or not, is by nature private from the public eye. As such, its occupation by inhabitants however social or its decoration by landscaping however intricate, would not invite impromptu deliberations or even mere interactions from passersby. The back patio is engineered to deter the cultivation of public- spiritedness, it is a refuge from the public in attempt to maintain privacy. The porch, by contrast, is an accidental venue for inviting nods of approval from passengers of carriages (121), impromptu deliberations by neighbours (compared to pre-planned neighbourhood coffees and bridge parties) (122), and quick greetings (122). These are all social interactions necessary in maintaining public-spiritedness. A love of the neighbor (referred to as ‘agape’ in the Bible), or the mere reminder of the humanity of the other requires the lived experience of social interaction. The porch has survived throughout millennia as a place for such interaction, and by extension: as the physical venue for cultivating public-spiritedness.

Encouragingly, Urban Genome Project member Khalil Martin’s research finds that the number of porches has dramatically increased in the past twenty five years. This disputes Richard H. Thomas’s theory of the porch’s decline amidst growing interest in back patios. Martin has found, using data from the U.S. Survey of Construction, that the proportion of American single-family homes that include a porch has increased from around 50% in 2000 to 64% in 2020. Furthermore, owner-built and contractor-built homes were consistently more likely to include a porch than homes built for sale or rent. This seems to indicate that people generally choose to have a porch when they can. 

Martin’s research finds that the porch continues to be recognized in North America to be an important social infrastructure and has gained status as “an icon for community and civic mindedness, through the spontaneous and liminal interactions it affords.” 

The American front porch has been used for a space for social rituals and ceremonies, such as summer tea rituals, courtship rituals, and seasonal events. Previously, American front porch has been used as a stage for performance and self-presentation, such as the various “porch campaigns” in early American politics, “porch concerts” (which also popularized during the pandemic), and even for social movements–for example when MLK preached on front porches. To add, the American front porch has also been used as a cultural signifier. Consider the adoption of Neo-classical porch styles by many statesmen, the mounting of national flags of porch posts, and other various style trends.


His research hopes to show how people have adopted, and adapted, threshold forms to meet their contexts and create collective identity. A further step is to also explore how the diversity and dynamism of threshold form features and uses relate to the notion of community thriving. Khalil frames his work as a means to “understand the opportunities for spatial agency and participation, in the urban context”

As a side note, Martin notes there may have been a decline in porch adoption between 1945 and 1995, but that data his research focused on ranged between 2000 and 2020.

Although the strength or spread of public spiritedness is difficult to measure, it should be encouraged on the basis of cultivating moral respect. I argue that greater consideration paid to the humanity of the other will bolster a sense of obligation to others, and consequently reduce partisanship and alienation common of large heterogeneous cities. Further thought should be devoted to porch-like spaces in public, vocational, and private spaces in the interest of supporting a good life for members of locational and vocational communities alike.

Upcoming Talk: Bernie Koch on The Evolutionary Dynamics of Cultural Change (As Told Through the Birth and Brutal, Blackened Death of Metal Music).

The Urban Genome Project at the School of Cities is hosting a talk next week by Bernie Koch on The Evolutionary Dynamics of Cultural Change (As Told Through the Birth and Brutal, Blackened Death of Metal Music).

This talk will be of special interest to those in the sociology of culture and computational social science, though it also has much broader import for general social theory and beyond . The talk will be on Thursday, February 3, 4:00 PM EST.

Please register by clicking here or by visiting this link:

We are looking forward to seeing you there!


How does culture change? We unify disconnected explanations of change that focus either on individuals or on public culture under a theory of cultural evolution. By shifting our analytical lens from actors to public cultural ideas and objects, our theory can explain change in cultural forms over large and long frames of analysis using formal evolutionary mechanisms. Complementing this theory, the paper introduces a suite of novel methods to explain change in the historical trajectories of populations of cultural ideas/objects (e.g., music groups, hashtags, laws, technologies, and organizations) through diversification rates. We deploy our theory and methods to study the history of metal music over more than three decades, using a complete dataset of all bands active between 1968 and 2000. Over the course of its history, we find strong evidence that the genre has been fundamentally shaped by competition between ideas for the cognitive resources actors can invest in learning about and reproducing this cultural form over time.

Speaker Bio

Bernard Koch is a PhD candidate in the sociology department at UCLA. Inspired by pre-graduate work in evolutionary biology and bioinformatics, his research now uses computational approaches to examine cultural dynamics in fields as diverse as science and music. In his work on culture, he seeks to wed theories of cultural evolution and cognition with formal models of population change from biology. Other projects elucidate how the culture and organization of scientific fields (e.g., machine learning, IQ psychology) create ethical and epistemic challenges. Lastly, he has broad interests in Bayesian modeling, machine learning, networks, and causal inference. His research has been published at NeurIPS, WWW, Sociological Methodology, and Science, among other venues.

Venues can unsettle sedimented patterns of segregation under certain conditions: addendum to “Venues and segregation: A revised Schelling model”

Generative models of urban form

In Venues and segregation: A revised Schelling model we demonstrate that venues can play a crucial role in shaping urban evolution, in particular through influencing broader patterns of integration and segregation. Due to space considerations, we could not include a key study in the paper.

This study investigates whether and how venues can diversify a segregated city after it a particular segregation pattern has become deeply entrenched. To answer this question, we first simulate a highly segregated city as an outcome of a standard Schelling process. Then we use a genetic algorithm to evolve the set of rules that would most decrease the degree of segregation. These rules include the location of venues, their exclusivity, and their degree of obligatoriness. In effect, the study evolves rules that would most dramatically alter the evolutionary direction of a city.

The study is below. See the original paper for more details regarding the parameters and graphical conventions, and simulation rules. 

Venues can unsettle sedimented patterns of segregation under certain conditions.

In this study, we demonstrate that the strategic placement of a new venue can unsettle sedimented patterns of segregation. This is important because one of the characteristics of the segregation patterns generated in Schelling simulations is that they are highly uni-directional processes. Once a set of individuals has become segregated, even a significant increase in their tolerance will not undo the neighbourhood divisions that have taken shape – barring any modifications to the internal psychology of individuals within the simulation. In this study, we show that venues can be used as an intervention within a settled Schelling model in order to disrupt the segregated outcome, without requiring any change to agents’ psychology. To do so, we add venues to a venue-less simulation that has already run its course and achieved a high level of segregated stability. In order to effectively determine what input parameters and venue positions will provide the most disruption, the two-dimensional parameter spaces used to explore earlier studies is not sufficient. Here we consider a range of venue positions, exclusivity, obligatoriness, tolerance, travel distance, and neighbourhood distance values simultaneously. In lieu of our prior interval based approach, we employ a Genetic Algorithm to test and recombine values for these parameters, evaluating different combinations in terms of how much they disrupt the initial condition (measured as a drop in concordance from the initial, segregated condition). An additional mechanism emerges, whereby one group’s venue establishes a “beachhead” into an area predominated by the other.

Figure 1 displays results. After running the algorithm with a variety of population sizes, mutation rates, and crossover rates, the progress of each evolutionary process is mapped as a sequence of fitness values to the chart in center of Fig 1.  Here, movement towards the right along each thread indicates the progress of the algorithm during one of its runs, while dropping values on the Y-axis indicate a reduction in the resulting concordance, i.e. a more successful solution. We select the most successful interventions in order to compare their values for each input parameter in the chart to the right in Fig 1.  Here, each notch along one of the spokes indicates a parameter value for one of the interventions, and hence, each intervention can be composed from a set of notches on each of the spokes.


Beginning from “Intolerance” and working clockwise through the spokes on Fig. 1, we consider the significance of the values arrived at for each, highlighting values that contribute to disruptive solutions. Overall, these solutions cluster around medium-low intolerance levels, high obligatoriness, middling exclusiveness, high catchment areas, a wide range of neighbourhood distances, and “beachhead” venue positions.

Intolerance: The intolerance values are clustered tightly around the value of 0.4 in successfully disruptive solutions. This value, just above the traditional Shelling tipping point, can be understood as a trade-off: it is high enough to motivate some movement by individuals, but low enough to support these same agents moving to an integrated rather than segregated destination.

Obligatoriness: The obligatoriness values tend towards 1 in disruptive solutions. Since obligatoriness controls the fraction of individuals that will feel compelled to visit venues, and since venues are the mechanism for disrupting the settled state, it follows that maximizing venue attendance will maximize the potential disruption. By contrast, introducing venues that inspire no obligation to attend them will do little to alter a segregated condition.

Exclusivity: Since exclusivity controls the number of other-group individuals who will consider visiting a venue, it regulates the new encounters between the segregated groups. It follows that an exclusivity of less than 1 is necessary in order to yield any new outcomes.  On the other hand, if the exclusivity is too low, any agents within the travel distance would visit and it would hence replicate the distribution of the surrounding area. Between these extremes, and in fact closer to an exclusivity range from 0.4 to 0.6, we have circumstances in which some individuals of the opposite group will be drawn into a venue, leading to a disruption when they find that after visiting they are no longer comfortable with their location. Thus maximizing disruption involves introducing venues that are neither too exclusive nor too open but rather those that exist in a “sweet spot” between the two extremes.

Neighbourhood Distance: The neighbourhood distance is the most dispersed of the non-location parameters, with all of its distribution occurring below a value of 4. We interpret this to imply that neighbourhood distance does not play a significant role in the outcome, so long as it is sufficiently low.

Venue Travel Distance: Unlike neighbourhood distance, the venue travel distance is very tightly clustered, and tends towards the highest value possible.  Since venue travel distance directly determines the number of individuals who can be affected by the venues, higher values naturally yield more disruptive results. Thus introducing venues with large catchment areas is likely crucial to interventions designed to unsettle existing patterns of segregation.

Venue Positions: Each of the two venues’ positions are encoded as an X and Y value between 1 and 50. This allows them to be located anywhere in the simulation world, even if this means displacing an individual from their initial condition. While their positions in successful solutions are mostly constrained to a narrow range, the X position of the first venue is something of an exception – with a whole range of positions that yield disruptions. In Fig 2, we summarize our findings for the venues’ positions by stepping through each cell, finding any simulations in which one of the venues occupies this cell, and colouring the cell according to the most disruptive outcome from among these simulations. In other words, we colour each square according to a best-case scenario of having a venue located there.  What results is a map of the most effective positions for locating venues.


Venues at “beachheads” are most likely to disrupt stable segregation patterns.Though the central map of Fig 2 clearly illustrates that there is a broad band of more successful venue locations along the boundary area between the two segregated groups, closer inspection reveals that ideal positions tend to be slightly embedded within one of the groups, rather than in the unoccupied space between. The tight clustering of values for the other parameters suggest that the successful disruptive runs are all variations on a single, emergent, strategy.  This strategy involves locating a relatively open venue of a group (G1) near to the edge but slightly embedded within the segregated neighbourhood of the opposite group (G2).  Because of the high maximum travel distance, individuals from the G1 are able to visit from farther away, while some closer agents from G2 are welcomed by the low exclusivity.  Upon visiting, these G2 agents become less comfortable with their location, since attendance has exposed them to a greater number of agents from G1. Simultaneously, the opposite dynamic is unfolding somewhere else in the simulation world. Because of this symmetry, individuals from both groups who feel compelled to move will find new locations opening up within travel distance to an appropriate venue, leading to an exchange between two areas of the simulation world.  Since the venue exclusivity is not too low, this exchange is not a complete flip – only the fraction of individuals who visit the opposite venue will relocate. These venues act like a “beachhead”, pushing away individuals from the other group and opening up spaces for their own agents to occupy. We can watch this same dynamic unfolding in the Video.


In this study,  we consider the possibility of applying our venue model as an intervention in highly segregated conditions. The success of the genetic algorithm in finding highly disruptive venue configurations speaks to the potential role for planning and design as a means of re-integrating a divided urban condition.  It must be stressed that the successful strategy described in this study is specifically tuned to the particular starting conditions that were used. Nonetheless, this study points at specific spatial relationships between segregated groups and disruptive venues as well as the crucial balancing of parameters such as intolerance and exclusivity. Further research would be necessary to generalize these results for other kinds of initial distributions of the simulated population.

New paper published! Venues and segregation: A revised Schelling model

Generative models of urban form


It goes without saying that most of our lives are spent in buildings. Less obvious are the implications of this obvious fact.

Consider a two-dimensional map. It presents a smooth surface, but the reality it represents is warped. Certain points on it support more interaction than others: the ones with buildings on them. Being near such a point puts you in close contact with more people than elsewhere. Depending on the social rules governing who is supposed to be there and what they are supposed to do, the building may increase or decrease your chances of coming into contact with people similar to or different from yourself.

They are not just physical structures, they are venues for social life, and the social order of cities grow up around them. If they change — their number and distribution, their rules of social inclusion or exclusion, the types of activity they afford — the city changes as well. This combination of forms, groups, and activities is the anchor of our model of urban evolution

In a new paper (with Ultan Byrne and Patrick Adler), we show via computer simulations the power of venues to affect the broader urban order by shaping the interactions of individuals. We do so by building upon the classic work of Thomas Schelling/ In 1971, Schelling proposed what became known as the “Schelling model of segregation,” which expressed in an especially clear way the type of thinking for which he eventually received the Nobel prize: local, small-scale interactions generate larger aggregate structures, often in surprising ways.

The “Schelling model of segregation” shows this vividly. Imagine a checkerboard with red and blue pieces that represent individuals. Let’s say each individual has a desire to be around people of their own group. Let’s make it relatively small: a red individual wants at least 25-30% of the others around them to be red, otherwise the’ll move to a different location where this condition is met, if they can.

Schelling showed that, starting from a random distribution of reds and blues, if you repeat this process over and over again you’ll end up with basically total segregation of red and blue. The map that results looks eerily like real cities.

The irony is that, within the Schelling model, no individual agent wants this outcome. The social structure is not necessarily a direct result of individual intentions. Moreover, once that pattern of segregation sets in, outside of a radical transformation of human psychology, little can be done to alter it (within this model).

This is a model and like any model it makes many simplifying assumptions. In our paper, we think through the implications of something maybe so simple that prior studies of this model have largely overlooked: there are no buildings in it, it does not capture the warped space we live in.

So we built a model that extends Schelling’s to include buildings in the simplest way we could think of. Basically, you need four things: 1. a travel radius (how far your reds and blues will go to visit the venue); 2. exclusivity (is the venue exclusive to one group, like an exclusive golf club, or is it open to members of any group); 3. obligatoriness (are individuals obliged to attend it, like an orthodox synagogue, or is it more optional, like a cafe); 4. physical features (how many venues are there, and where are they located).

With those simple features, you can account for, and observe the logical implications for urban segregation and integration, of one of the most pervasive facts of our experience, which is that we congregate in buildings. This happens because the people you interact with in buildings alter the Schelling-style calculation as to whether an individual feels “comfortable” in their location. One might be a majority in terms of the people who live nearby or who you pass by on the street, but a minority when you include those you meet in the venues. Or vice versa: you might be a minority in terms of who lives there, but interact with many people of your group in the local venues (who traveled there from elsewhere) or travel elsewhere to interact with members of your group.

By repeating and varying those simple processes you can think through their implications. One is that they generate a distinctively urban order: Schelling’s model yields clumps whose physical location has no meaning or basis. With buildings in the model, you can generate an East vs. West side (“opposite sides of the tracks”) or a centre-periphery structure with a more diverse core and more homogenous peripheries.

You can also observe how, depending on the characteristics and location of the building, it is possible to forestall the deep segregation characteristic of the Schelling model from arising, without requiring any radical transformation of individuals’ psychology. You can also unsettle deeply sedimented patterns of segregation through the right combination of venue parameters, whereas they are basically set in stone in Schelling’s highly individualistic model (via a genetic algorithm, not shown in this paper but coming to a blog post soon)

And you can find ironies and reversals like the sort Schelling exposed. Just as Schelling demonstrated that one cannot simply read individual intentions from collective patterns of behavior, one cannot simply read organizational values from their surrounding patterns of segregation. Relatively exclusive venues can generate diverse neighborhoods (by providing a local foothold for minority groups to sustain their distinctive cultures), while relatively inclusive venues can in some circumstances produce highly segregated areas (by drawing in tolerant and “adventurous” persons who, despite their individual understanding, change the overall makeup of the area).

An advantage of the computer simulation approach is that you can pinpoint the precise mechanisms by which these outcomes occur. Some of these include “evacuation,” “cooptation,” “bootstrapping,” “cascading,” and “bridging.” 

The paper also includes videos showing the simulation runs unfold. 

The abstract is below. The paper is freely available here.

Abstract: This paper examines an important but underappreciated mechanism affecting urban segregation and integration: urban venues. The venue- an area where urbanites interact- is an essential aspect of city life that tends to influence residential location. We study the venue/segregation relationship by overlaying venues onto Schelling’s classic (1971) agent-based segregation model. We show that a simulation world with venues makes segregation less likely among relatively tolerant agents and more likely among the intolerant. We also show that multiple venues can create spatial structures beyond their catchment areas and that the initial location of venues shapes later residential patterns. Finally, we demonstrate that the social rules governing venue participation alter their impacts on segregation. In the course of our study, we compile techniques for advancing Schelling-style studies of urban environments and catalogue a set of mechanisms that operate in this environment.

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