/mixed-uses
1st May, 2021Gareth Simons

An evaluation of mixed-use measures and methods for their application at the pedestrian-scale

Abstract

Mixed-use urbanism affords access to diverse assortments of landuses within a pedestrian-accessible context, and confers advantages such as reductions to driving, air pollution, and Body Mass Index, with associated increases in the use of active transportation and improvements to health. Whereas mixed-use urbanism is clearly beneficial, methods for measuring and assessing the presence of mixed-uses at a granular level of analysis remain murkier: use of larger-scale aggregational workflows can cause a loss of contextual spatial information with the implication that inferences can’t be meaningfully projected to the context of street-fronts without invoking the ecological fallacy.

This work demonstrates techniques for gauging mixed-uses in more spatially precise terms concurring more readily with an urbanist’s conception of pedestrian-accessible mixed-uses. This is addressed through the use of the cityseer-api Python package which facilitates use of spatially granular landuse classification data which is assigned to adjacent street edges and then aggregated dynamically, with distances measured from each point of analysis to each accessible landuse while taking the direction of approach into account. This methodology is used to probe established diversity measures, including Shannon, Gini-Simpson, and Rao / Stirling indices to develop an intuition for how these indices work and whether they behave suitably as a measure of mixed-uses. It is argued that Hill Numbers is a more suitable measure of diversity because it can be configured to mirror the intent of the traditional indices while transforming these into the unit of true diversity which scales intuitively when applied to larger aggregations of landuses; further, distance-weighted formulations of Hill diversity can be applied with spatial impedances, thus conferring a particularly spatially-nuanced gauge of local access to mixed-uses.

These methods and indices are demonstrated for Greater London using the Ordnance Survey Points of Interest dataset consisting of 388,323 points spread across 616 classifications. These are assigned to adjacent streets derived from the Ordnance Survey Open Roads dataset and then processed using distance thresholds ranging from 50m to 1600m. The observations are then correlated to Principal Component Analysis derived from a range of landuse accessibilities measured from the same locations and for the same point-of-interest dataset. The Hill diversity measures, particularly the distance-weighted formulations, offer the strongest correlations for both wider mixed-use districts and for more local ‘high-street’ mixes of uses, while yielding the most intuitive and spatially precise behaviour in the accompanying plots.

Link to preprint paper pending.

Introduction: Mixed-uses, modernity, and suburbia

The agglomeration of people is, of necessity, underpinned by a substantial complexity of interactions, and this is reflected in the variety and propinquity of landuses afforded by urbanisation1|2. The evolution of mobility and communications technologies has dramatically intensified and fragmented these dynamics across space, yet has not nullified the beneficial aspect of geographic proximity nor the human desire for contact and a sense of place3|4. Within the context of urbanism, the term mixed-uses refers to assortments of diverse landuses facilitating varied assortments of interaction, but with the specific connotation that these should be available to pedestrians at the local scale. This is, in effect, a pedestrian-first rather than car-centric premise for urban connectivity and should not be construed as nostalgia for traditional neighbourhoods or idealised small-town living. This also does not mean that all locations will necessarily be within walking distances; for larger towns and cities, many locations may not be directly reachable by foot but can still be accessed by pedestrians through the complementary use of transit or active transportation.

The interconnection of landuses has always been desirable and prevalent through the history of urbanisation; yet, a thorny issue for planners has been that revolutionary forms of personal motorised transportation and the emergence of communications technologies led to the assumption that it was possible, even preferable, to sustain these interactions purely at the larger-scale and that it was acceptable to do so at the expense of local pedestrian connectivity. First triggered by the emergence of commuter railways, early instances of landuse separation promised an escape from the squalor of industrial cities to the ‘slumless’ and ‘smokeless’ satellite suburbs idealised by the Garden City Movement. Though finding support in early modernist planning philosophies5|6 it would be the mass-production of cars that would ultimately fuel the increasingly blatant and indiscriminate separation of landuses, ultimately finding its most pathological expression in post World War II American suburbia7.

The history of suburbia veers into a broader discussion of modernity and the destabilisation of traditional identities, a pervasive search for a sense of place and belonging, and the collective pursuit of private interests. Early 20th century sociologists documented a momentous societal shift from a predominately rural to urban state of existence in western societies. Traditional folk society, typified by small and familiar, often isolated, and culturally homogenous towns and villages with a strong sense of solidarity8 gave way to an increasingly urbanised existence characterised by greater social anonymity and exposure to heterogenous assortments of cultures and ideas. This process is often envisioned in one-direction, the swelling numbers of city-dwellers recruited from the countryside and bearing the imprint of a rural past; yet, the opposite effect also held true, rural dwellers were increasingly affected by forms of culture and technology emanating from cities9. Relentless development of mobility and communication technologies expanded spheres of social and economic interaction, with the consequent intensification of interactions shifting relationships away from the realm of the familiar into the desensitised state of the blasé: impersonal, segmented, and superficial with qualitative distinctions increasingly reduced to monetary terms10. Rapid urbanisation thus presented a paradox, it was at once both liberating and deeply unsettling. Traditional communities had offered a strong — albeit prescriptive — sense of identity and a more stable — albeit geographically confined — sense of place and belonging. Cities, on the other-hand, implied a more fluid and competitive dynamic emerging from an unstable equilibrium maintained through mobility and continual adaptation. Identity now had to be constructed from transitory assemblages of ideas, people, and places11|12. This provoked a collective sense of loss and nostalgia for a past life idealised as simpler, geographically anchored, and socially homogenous, beacons of meaning and security in a world beset by constant change4|13.

City dwellers were thus faced with a dilemma: they were repulsed by the estrangement and perceived evils of urban life yet were attracted to the opportunities afforded by urbanisation. Suburbs are, in effect, an attempt to synthesise this dichotomy through the collective pursuit of individual interests behind the facades of harmony with nature and close-knit stable communities7. Access to cheap land coupled with the mass-production of cars subsequently unleashed the leap-frogging suburban development that has become a ubiquitous template: sprawling and fragmented assemblages of low-density, single-landuse-zones patch-worked together by motorways. Though recent planning policies may give a different impression, these patterns remain tangible and feature in contemporary forms of urban development around the world. By way of example, a 2018 report based on a qualitative review of new housing developments in the United Kingdom found car-based living; homes not properly connected for pedestrians, cyclists, or busses; missed opportunities for public transport; and a lack of mixed-uses14.

A twist of irony remains. The suburban ideal imploded into suburbia, an unanchored and endlessly repeating stream of motorways, malls, and fast-food signs, exuding an all-pervasive sense of placelessness that only exacerbated the sense of loss predicated by modernity12|13. A consequent backlash against suburban planning emerged in the form of New Urbanism, a set of planning principles based on traditional neighbourhoods prevalent before the widespread emergence of suburbia, broadly advocating the use of public spaces, mixed landuses, pedestrian friendly design, and the clear articulation of public and private spatial thresholds15|16|17|18|19. Whereas these design principles are generally sound, New Urbanism also echos the now familiar refrain: the desire for a sense of place and community associated with the past, and the notion that the replication of traditional neighbourhood design principles leads to stronger local communities. As such, New Urbanism has been prone to pastiche due to a tendency to conflate the concept of community, in the wider sociological sense of the word, with that of the neighbourhood, a smaller subset of geographically anchored social interactions20|4. Whereas traditional neighbourhood design principles may encourage casual and neighbourly social interaction21|22, these do not necessarily lead to deeper social bonds solely on the basis of propinquity23|24|25|26|27.

Quantitative support for mixed-use development is emerging around themes pertaining to reductions in driving, air pollution, and Body Mass Index, as well as increases in the use of active transportation, and improvements to health28|29|30|31|32. Potential benefits to local economic vibrancy and the resilience of neighbourhoods, as advanced by33, tend to remain less developed and present a rich avenue for exploration. Unlike road networks, which evolve slowly and rarely change, granular mixed-use districts adapt comparatively quickly in response to evolving economic opportunities and constraints: a reflection of underlying complex-adaptive urban systems and their capacity for resilience through feedback and adaptation — otherwise incapacitated by the crude brush-strokes of abstract urban planning34|35|36.

Link to preprint paper pending.


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