The Virtual and the Real in Planning and Urban Design by Yamu Claudia;Poplin Alenka;Devisch Oswald;De Roo Gert;

Author:Yamu, Claudia;Poplin, Alenka;Devisch, Oswald;De Roo, Gert;
Language: eng
Format: epub
Publisher: Taylor & Francis Group

Explaining centrality and measuring accessibility

According to Hillier et al. (2007), cities have a dual nature, with both a foreground and background network. The foreground global network reflects the micro-economic functional pattern. It is the general component of the city and works in the same way independently of any particular culture. For example, the location pattern of shops is attracted to the spatially most integrated streets on various scale levels. The foreground network links urban centres at all scales to each other. In general, the foreground global network gives a European, historically grown city’s street structure a deformed wheel pattern. The main routes of the network that pass through urban areas hence shape the deformed wheel’s armature. In this way, accessibility, from the city’s edges to its centre, and the natural interface of co-presence through movement from centres to edges, is made efficient and possible.

Within this network, the growth of settlements entails a reorganization of spatial systems, including the hierarchy of centres and sub-centres, or ‘centrality’ and ‘periphery’. Centrality has been revealed as an important factor in understanding the structural characteristics of a complex relational network. It is also relevant to various spatial factors affecting social activity in cities. Centrality, or rather the cascade of different-sized centres, as well as centre and periphery, represents the hierarchical scale of accessibility within a system. Hillier redefined ‘centrality’ as ‘pervasive centrality’ (2012), whereby centrality functions in a diffuse manner throughout the network on all scales (closeness and proximity to smaller and larger centres from a certain location within the city). In this context, space syntax has made the link between the emergent structure and spatial agency, where a city’s emergent structure is a law-governed process concerning the network of spaces linking buildings together (morphological component) and, in turn, the emergent spatial structure itself has effects on the functional patterns of the city.

At first sight, centrality seems to be something static, and the central area and its boundaries well defined, requiring only the study of the spatial-economic layout. However, when adding temporal aspects, the idea of a stable and clear centre fades: centres shift, expand, shrink or change their focus – and all this occurs in a non-linear manner. Human behaviour, expressed in choices made (e.g. shopping, travel behaviour), also influences the spatial form and plays a role in the constitution of centrality. Space syntax measures the idea of centrality using two logics: ‘integration’, representing ‘to-centrality’, and ‘choice’, representing ‘in-between-centrality’.

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