Complexity In Urbanism
Complex systems theory consolidates developments that have emerged out of several fields spanning evolutionary theory, computer science, information theory, and network analysis. There is some debate about whether and how ‘Complexity Science’ should be defined1, with attempts at formalisation broaching conceptions such as size, entropy, algorithmic information content, logical depth, statistical complexity, fractal complexity, and hierarchical complexity (Mitchell, 2009. pg. 96–100)2. More simply, complex systems can be characterised as collections of agents demonstrating emergent dynamics; thus, systems “in which large networks of components with no central control and simple rules of operation give rise to complex collective behavior, sophisticated information processing, and adaptation via learning or evolution”2 (pg.13, 94). The now prevalent application of complex systems theories to cities3|4|5 heralds a shift in conception from static to dynamic and from top-down to bottom-up, in effect recognising cities as out-of-equilibrium systems that can exhibit difficult to predict emergent phenomena.
Earlier rumination on these themes can be traced back to three prominent urban theorists. The first, Patrick Geddes, initially trained as a biologist and used ecological metaphors to describe the complex processes he observed in cities. He advocated conservative surgery consisting of contextually appropriate and smaller-scaled planning interventions that are sensitive to bottom-up evolutionary dynamics6|7. Though unappreciative of Geddes’ background and thinking, this theme was subsequently developed by Jane Jacobs who insisted that small-scale particularities and ‘unaverages’ — obscured by aggregate statistical methods — are of critical importance to the understanding of how cities work. She argues that any analysis of cities must proceed from “particulars to the general, rather than the reverse” and that it is necessary to “seek for ‘unaverage’ clues involving very small quantities, which reveal the way larger and more ‘average’ quantities are operating” (Jacobs, 1961. pg. 440)8. In associating particularities with the emergent and dynamic systems-level processes they generate, she makes the first explicit link from The Kind of Problem a City Is to cities as complex systems. A complementary argument was put forward by Jacobs’ contemporary, Christopher Alexander, who argued that modernist approaches to problem-solving in architecture and urban planning were reductionist and resulted in inferior outcomes compared to traditional methods, wherein incremental and iterative feedback processes — akin to contemporary conceptions of complex systems — generate successful solutions in the form of time-tested traditions9 (this notion need not necessarily be conflated with the traditionalist aesthetic interpretations advocated by some of Alexander’s more ardent adherents).
Implicit within Jacobs’ and Alexander’s hypotheses is the notion that cities are systems of networks energised by diverse assortments of functions, thus presaging a contemporary complex systems interpretation of cities that goes beyond strictly spatial and visual conceptions of urban space to one that explicitly acknowledges the flows engendered by those spaces. Cities can thus be described as “constellations of interactions, communications, relations, flows, and networks\ldots location is, in effect, a synthesis of interactions”10 (pg.13, 15). This view denotes a dynamic interpretation of cities complete with feedback processes, self-organisation, and emergent behaviour. This can be difficult to reconcile with the intentionality of urban masterplanning, which favours the abrupt imposition of large and rigid spatial arrangements that can incapacitate the more gradual and contextual self-organising character of cities as evolutionary artefacts11|12|5. This conundrum is represented in its most extreme form in the low-density sprawl of North American suburbia, the characteristics of which represent a complete inversion of the dynamics exhibited by more incrementally developed cities: buildings detach from their surroundings by focusing inwards and minimising spatial and functional integration with adjacent streets (as typified by garage-lined residential cul-de-sacs, office parks, and big-box stores); road networks are designed to selectively connect distant places at the expense of local connectivity, resulting in fragmented spaces where social and functional integration is discouraged or, in extreme cases, specifically prohibited by gated communities; and, streets and interstitial space cease to function as spatially connective tissue and have little social or functional capacity for use as public space13|14|15|16|17|18|19.
Jacobs and Alexander posit that urban planners can take specific morphological characteristics into account which allow evolutionary forms of urban dynamics to unfold unimpeded across space and time. These approaches are arguably replicable in new development by following principles broadly encapsulated by Jacobs’ ‘generators of diversity’, and as echoed in various incarnations of contemporary urban design philosophies. It should be cautioned that a direct simplistic link between the spatial form of cities and their social and economic characteristics is not to be assumed, and that these design principles should instead be envisioned as permitting rather than coercing the consequent dynamics. Therefore, whereas sufficiently fine-scaled, mixed-use, and densely interconnected urban environments can support large sets of combinatorial possibilities across space, the exact expression of these configurations arise from bottom-up processes as they unfold, or, if initially imposed in the form of masterplans, should be permitted to adapt over time in response to evolving pressures. For the same reason: dense, walkable, and mixed-use urban substrates are not necessarily at odds with the advent of changes such as online shopping and services; on the contrary — and unlike suburbia’s hegemonic shopping malls — granular substrates have substantial capacity for resilience because they permit incremental adaptations as the nature of spatial networks changes over time, for example, towards social and specialist services, e.g. coffee shops, boutique stores, eateries, local grocers, convenience stores, post-offices, etc., and away from traditional services now better delivered through online interfaces, such as banks and department stores. In this sense, urbanism can be likened to computational substrates resembling cellular automata20|21. Suburbia represents one extreme, an amnesiac non-computational state in which the ‘fast dynamics’ — flows of urban energy generated by social and economic activity — remain detached from the ‘slow dynamics’ of the urban fabric. These are brittle substrates: they take tremendous energy to create or change, and therefore have no capacity to adapt in response to small fluctuations accumulating through time. Conversely, a complex systems approach can be likened to a computational state wherein “the fast dynamics of the flows are successfully coupled to the slow dynamics of long-term adaptation and evolution” (Holland, 1995. pg. 166)22. This slow-fast coupling of information allows the feedback over time between the urban substrate — the mix and intensities of landuses — and the flows of energy that unfold through these spaces, thus permitting co-evolution to what can be thought of as an edge of chaos wherein streets, neighbourhoods, and districts compete to seek-out and harness the flows and their endless permutations evolving through time.
Applied judiciously, complexity theories offer a means to bridge the sometimes disjointed qualitative and quantitative approaches towards cities5. Importantly, a complex systems lens provides a substantive theoretical basis underpinning qualitative interpretations of urbanism while providing a link to the quantitative methods that are further developed in this work; specifically, street network centrality methods derived from network science and mixed-use measures derived from information theories, which are here viewed from the perspective of proxies of the potential for complex cascades of interactions to unfold across a given urban substrate.
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