Revealing the Changing Spatial Structure of Cities from Human Activity Patterns

Identifying changes in the spatial structure of cities is a prerequisite for the development and validation of adequate planning strategies. Nevertheless, current methods of measurement are becoming ever more challenged by increasingly dispersed forms of urban organisation. Being motivated by the recent availability of large-scale data on human activities, this paper proposes a new quantitative measure for the centrality of locations, taking into account both the number of people attracted to different locations and the diversity of their activities. This ‘centrality index’ allows for the identification of functional urban centres and for a systematic tracking of their relative importance over time. As a case study, the proposed index is applied to extensive travel survey data in Singapore for the years 1997, 2004 and 2008. It is shown that, on the one hand, the city-state has been developing rapidly towards a polycentric urban form that compares rather closely with the official urban development plan. On the other hand, however, the downtown core has strongly gained in importance, and this can be largely attributed to the extension of the public transit system.