The world is both urbanizing and on an unsustainable trajectory. Consequently, industrialized societies must urgently address the dual issues of catering to the urban populations’ well-being and ease the cities’ pressure on the planet. Urban form can constitute a key leverage point; it matters for many physical health outcomes (Goines and Hagler, 2007; Tan et al., 2010; Marshall et al., 2014; Sarkar et al., 2017; Borck and Schrauth, 2021) and many mental health outcomes (Evans, 2003; Barros et al., 2019; Hunter et al., 2019). It also matters for mitigating climate change (Creutzig et al., 2015; Güneralp et al., 2017; Barrington-Leigh and Millard-Ball, 2020) and the sixth mass extinction (Seto et al., 2012). The aim of this paper is to propose measurable principles for urban form that promotes subjective well-being and at the same time align with efforts to mitigate cities’ environmental impacts. Subjective well-being is an important part of human well-being (Dolan and Metcalfe, 2012) that encompasses affective and cognitive processes (Pavot and Diener, 2013) and can be conceived as resulting from an individual’s resources and challenges in the psychological, social and physical domains (Dodge et al., 2012). There is a long tradition in urban discourse to implicitly adhere to this conception of subjective well-being by describing city life as integrated social and psychological phenomena that play out across physical space. In 1903, Simmel described how the intensification of economic activity and environmental stimuli in the rapidly growing metropolises of its day caused behavioral adaptations in the social domain (Simmel, 2002). Wirth (1938) outlined the sociological concept of city in which personal relationships are partly replaced by institutions catering to the masses. Milgram (1970) argued for adaptation to sensory overload as the mechanism behind the emergence of specifically urban behaviors, such as allocating little time to each interpersonal interaction. These works constitute milestones in a line of thinking centered around the tension between social and economic resources and psychological challenges in urban life.

There is also a long tradition in urban discourse of prescribing idealized urban forms that aim to balance the social and economic opportunities of city life with access to health-promoting open space. This was true of the garden city movement (Howard, 2007), as part of which Perry (1929) devised the neighborhood unit plan that was the model for several designs by architects Henry Wright and Clarence Stein. It was also true of the modernist school of thought, in which Le Corbusier developed a vision of a city of towers encircled by parkland that would meet the needs of modern business while avoiding the noise and pollution associated with pre-modern cities (Le Corbusier, 1986). However, propositions such as these largely disregarded existing spatial and social dynamics, the dangers of which was best expressesd by Jacobs (1961) in The Death and Life of Great American Cities. As a counterpoint to idealized prescriptions for urban form, space syntax (Hillier et al., 1976) emerged as an analytical framework to systematize descriptions of urban space by studying how human settlements evolve bottom-up. The approach convincingly revealed how the ways in which humans configure space manifest a social logic that embeds social and economic processes, and that such dynamic processes can in part be captured by static descriptions of urban form (Hillier and Hanson, 1984; Hillier et al., 1993).

The development of space syntax research has been part of a general surge in recent decades in quantitative spatial analysis of cities that have extended beyond urban form alone and into areas more directly related to subjective well-being. Recent methodological advances have resulted in rich quantitative evidence for how people move through, behave in and experience urban space. Thus, urban form might increasingly be able to function as a focal point for different strands of research that deal with sustainable urban life. Moreover, research can be better linked with planning practice through the development of empirically informed principles for urban form. In cities in industrialized societies where urban landscapes are largely shaped by formal planning processes, such empirical principles could serve an urban planning paradigm aiming to promote inhabitants’ subjective well-being as well as ease cities’ pressure on the planet. To underpin the principles I propose here, I synthesize in a non-systematic review recent findings from urban morphology, complex systems analysis, environmental psychology, and neuroscience. This literature is presented as three different perspectives on urban form and subjective well-being: the socio-spatial perspective, the psychological perspective and the bird’s eye perspective. The integration of perspectives in this text means that it cannot present all the intricacies of any particular research area; the purpose is instead to make manifest relations between different phenomena relating to subjective well-being in urban life. I then present three principles revolving around the concept topodiversity, and how they together suggest an urban form that I call the topodiverse city. Lastly, I propose some indicators that can be used to measure the principles and the relevant outcomes related to them.

Cities are about facilitating human interaction in physical space (Batty, 2012). The primary medium of this is the street network, where those spaces that facilitate interaction can be thought of as a foreground network contrasted against a background network of mainly residential space (Hillier et al., 2009). Humans do not roam a street network randomly: research rooted in complex systems analysis has shown that they tend to move between a few select places that together make up an activity set and where the visitation frequency of places follow a power law distribution (González et al., 2008). This conserved range of mobility means that as humans explore novel places there is a possibility that these places become part of the activity set while familiar places are dropped from it, and so the activity set evolves over time (Alessandretti et al., 2018a). The size of the activity set and the degree to which one engages in exploration varies considerably between individuals, and covaries with personality traits like extraversion (Alessandretti et al., 2018b); however, many day-to-day activity sets encompass ∼25 places (Alessandretti et al., 2018a).

The locations of places in the activity set together with routes between them constitute an activity space (Cagney et al., 2020). Just as activity place set sizes varies between individuals, so does activity space sizes (Hasanzadeh et al., 2018). An early observation in space syntax research was that movement between places tends to occur along the topologically shortest route connecting those places, or in other words that people tend to make as few turns as possible (Hillier et al., 1993). More recent studies have achieved better predictions by weighting turns by their angles, meaning that people tend to take routes where the total sum of angular direction change is minimized; this has for example been verified by microscale tracking of ∼2 million urban pedestrian trips through mobile phone wi-fi signals (Stavroulaki et al., 2019). Corroborating evidence has also been uncovered through neuroimaging that reveals how during navigation in a city some parts of the hippocampus track changes in local topology while other parts track the current place’s prominence in the global network (Javadi et al., 2017). Such tracking is possible because the visual system continuously identifies possibilities for moving across the environment (Bonner and Epstein, 2017), or in other words links in the topological network. Topological structure is crucial for navigation because it answers the question “From the current place, which other places can I move to?” This means that topologically central places will be more attractive locations for example when establishing a business, as more movement en route to other places will happen there. Thus, the distribution of destinations often acts as a multiplier of the movement patterns generated by the street network (Hillier et al., 1993).

Street network characteristics also influence travel mode choices. On this topic, little research has focused on topological street network structure. However, networks with high intersection density (which is not a topological measurement) favor walking and biking (hereafter “active movement”) (Marshall and Garrick, 2010). In fact, such street network characteristics seem to matter more than residential or job density (Ewing and Cervero, 2010). In industrialized societies, less connected street networks and lower built densities are independently associated with higher degree of car ownership (Barrington-Leigh and Millard-Ball, 2019). Thus, how the street network is designed will influence the activity spaces of individuals (Parthasarathi et al., 2015), both directly by determining modes of transport and routes taken for travelling between places, and indirectly by what spaces it privileges for establishing economic or social activity. Furthermore, because humans have a limited mobility range (Alessandretti et al., 2018a), these activity spaces will be “sticky” once they form. This makes the configuration of the street network a powerful tool in the structuring of urban social and economic life.

The previous section describes a positive feedback loop: where more people move, more activity will take place, making even more people move there. This is reflected in aggregated movement flows being exponentially related to the topological centrality of streets (Hillier et al., 1993). Characteristics at the systemic level thus feed back to the local place level in that the flow of people will influence an individual’s experience. For example, in Stockholm’s areas of high topological centrality, experiences with negative valence, often related to crowding, dominate (Samuelsson et al., 2019). This is what Milgram (1970) argued specifically urban behaviors to be an adaptation towards. Yet, such adaptations might not always be sufficient to cope with environmental demands. Appraisal of the environment can cause a psychophysiological stress response if the situation is perceived to frustrate control or contain the possibility of negative social evaluation (Dickerson and Kemeny, 2004). The intimate connection between city life and a social stress response is corroborated by experimental evidence (Lederbogen et al., 2011) exposure to concentrated movement flows could be a key factor for this connection (Samuelsson et al., 2019). New methods utilizing smartphones and other wearable sensors for tracking people moving through urban environments while collecting subjective and objective indicators of their experiences (e.g. Shoval et al., 2018; Torku et al., 2021) could, if combined with street network measurements, further research around what the systemic spatial conditions are that create stress in urban life.

Seeking out environments with a relative absence of stressors, which in modern cities often correspond to natural settings, allows for affective and cognitive restoration (Hartig et al., 2003). Out of the many health benefits of nature experience that research has highlighted, the restoration pathway is one of the most central and well established (Markevych et al., 2017). For example, spending an hour in natural settings in one’s daily urban life reduces salivary stress hormone concentrations by about 20% (Hunter et al., 2019). The benefits of nature experience for subjective well-being has contributed to a growing interest in urban greening and biophilic urbanism, a design approach that seeks to integrate natural elements with the built urban fabric and erase the unhelpful dichotomy between city and nature (Reeve et al., 2015). Such design approaches hold great potential for reducing stress responses at or close to their source (De Vries et al., 2013), and for improving other urban ecosystem services (Abhijith et al., 2017; Kong et al., 2017), and should consequently be a key urban redesign priority. Nevertheless, a requirement of fully restorative environments is that they provide getting away from one’s routine (Hartig et al., 2003), so it comes as no surprise that restorative experiences happen in areas with the least topological centrality (Samuelsson et al., 2019). In other words, urban inhabitants often have to literally go out of their way for restorative experiences. Depending on urban form, this requires different amounts of effort for the individual seeking restoration.

Taken together, the above paragraphs paint a gloomy picture of urban life. Yet, cities are celebrated for concentrating a wide variety of people and activities. In this vein, longitudinal data shows that experiencing different places in a day leads to positive affect in individuals, especially if these places are sociodemographically varied (Heller et al., 2020). Furthermore, there seems to be a feedback relationship in that positive affect also encourages people to seek out novel environments (Heller et al., 2020). Street network configuration underpins possibilities for social co-presence in public space (Legeby, 2013). Furthermore, active movement, compared with driving or public transport, invite richer sense experiences of the routes traveled and interactions with the environment that can build social connectedness (Brömmelstroet et al., 2017). Active movement is also related to more positive mood compared with motorized transport (Glasgow et al., 2019), but it remains to be researched how transportation mode mediates associations between environmental diversity and subjective well-being. Across different people, the diversity of kinds of experience within the same neighborhood is greatest in areas of intermediate centrality, as opposed to the most connected areas that are dominated by negative experiences (Samuelsson et al., 2019). Such evidence suggests the possibility of urban environments that promote subjective well-being through access via active movement to the cities’ varied social and economic resources while avoiding the psychological toll of crowding.

In complex adaptive systems, such as cities (Batty, 2009), emergent properties arise from local interactions (Levin, 1998). With increasing availability of very large datasets on various aspects of cities and urban life, there has been a growing interest in recent years of extracting “universal laws” out of the emergent properties arising from local social and economic interactions. While we cannot expect to ever reduce geographical phenomena to fully replicable laws (Goodchild and Li, 2021), it is helpful to uncover links between the eye level view of the inhabitant and the bird’s eye view because it 1) helps understanding what processes that give rise to specific urban forms, and 2) is a requisite for complexity-based empirically informed ideas about urban form that answer to the outcomes we care about.

Again, cities’ reason for being are facilitation of human interaction in physical space (Batty, 2012). This is reflected in urban scaling laws: street network length scales sub-linearly with population size whereas social and economic activity scale super-linearly (Bettencourt, 2013). These spatial interaction effects enable coordination of knowledge that explains why complex economic activities concentrate in large cities (Balland et al., 2020).

Infrastructure length and socioeconomic activity also scale in a hierarchical way among the sub-areas within cities, which can be explained by spatial autocorrelation of socioeconomic activity (Dong et al., 2020). In other words, the positive feedback mechanism that activity attracts further activity shows up yet again. The relative configurational properties of street networks within this hierarchical arrangement tend to remain constant with changing city size (Hillier et al., 1993), suggesting that hierarchical scaling maintains the street network’s ability to continue to facilitate human interaction in the face of growth. These observations are in line with a recently proposed visitation law of human mobility (Schläpfer et al., 2021). The authors find hierarchical spatial clustering of economic activity arising from individuals’ movement being constrained in space and time and simultaneously coupled with each other (i.e. activity attracts further activity) (Schläpfer et al., 2021). This explains why many cities, especially those dating from pre-modern eras, display macroscale fractal morphologies (Makse et al., 1995); a fractal form arises as an emergent property resulting from decentralized self-organization because it gives more interaction bang for the spatiotemporally constrained travel buck. Thus, human mobility is not scale-free; it is structured in “spatial containers” that correspond well to intuitive conceptions of neighborhood, city, metropolitan area and region (Alessandretti et al., 2020). The same spatial scales can be found in the topological configuration of street networks (Berghauser Pont et al., 2017). These findings are reminiscent of central place theory (Christaller, 1933), a conjecture in geography which similarly posits that a spatial hierarchical clustering of economic centers optimizes traveling among a population.

In summary, a convincing body of evidence now indicates that urban systems self-organize towards maximization of human interaction given travel costs. Yet, this does not necessarily equate a desired output in terms of human well-being, as the section on the psychological perspective above illustrates. Neither does it necessarily equate mitigation of cities’ impacts on the planet. I now turn my attention to how urban form can contribute to these dual outcomes.

The story so far has been one of urban form emerging bottom-up from local interactions. While this is how pre-modern cities grew, urban development in industrialized societies is just as much about top-down urban planning interventions. Modernism’s all too heavy-handed counteractions towards urban bottom-up dynamics was a central theme in Jane Jacobs’ classic The Death and Life of Great American Cities (Jacobs, 1961). A better paradigm in urban planning should work in accord with the central dynamics of cities’ emergence. The research recounted in the preceding three sections illustrates a few broad categories of system component that produce these dynamics. There is a mutualism of co-evolving network and destinations. This co-evolution influences movement flows. Furthermore, it takes place in a geographic context, including a natural landscape that the network can provide access to or shield people off from. These components together create spatial conditions for environments to support subjective well-being (Samuelsson, 2021), where certain spatial conditions support subjective well-being through certain pathways. For example, spatial conditions in the foreground network better support well-being through possibilities to partake in social and economic activity (cf. Hillier et al., 2009) whereas those in the background network better support well-being through restoration.

I propose the term topodiversity (from the Greek topos meaning place) to refer to variation across an urban area in such spatial conditions that matter for subjective well-being, so that it can be promoted through several different pathways (Samuelsson, 2021). The term highlights how distinct places support subjective well-being but that the ways in which they do so is conditioned on them being parts of a larger spatial system. Urban planning should shape urban form so as to improve or maintain topodiversity while at the same time limit cities’ environmental impacts. It is with these dual goals in mind that I outline three general principles for topodiversity below, before illustrating how they together suggest an urban form that I call the topodiverse city and compare it to the dense city and the sprawling city.

Keeping an increasingly urban civilization healthy and happy within environmental planetary boundaries requires urban environments that allow both for sustainable social and economic interaction and psychological restoration, the ebb and flow of urban life. Frameworks that lead the way should be malleable enough for context-sensitive application in urban planning, yet rigorous enough to lend themselves to scientific inquiry. I have proposed three principles along these lines, revolving around the concept topodiversity, that are intended to balance sprawling and concentrating forces in cities (Principle 1 and Principle 2), and ensure support of subjective well-being through multiple pathways on the neighborhood scale (Principle 3). The principles together point towards the topodiverse city as a desirable urban form distinct from both the dense city and the sprawling city. Nevertheless, the principles are far from suggesting rigid idealized solutions that disregard existing dynamics; they rather stake out a direction for stepwise development based on the context and the socio-spatial system of the city. Importantly, fulfilment of the principles can also be measured using data and methods that are already existing and to a large extent openly available. The principles can consequently be related to actual movement and subjective well-being through ubiquitous technology like smartphones. Such methodological integration finally allows a sort of quantitative and analytic succession to classical works like those by Simmel (2002), Wirth (1938), Jacobs (1961), and Milgram (1970). I hope to see future research investigate how the principles hold up under scrutiny, and more closely determine what spatial organizations characterize the topodiverse city in different contexts.