Re-evaluating polycentric urban structure: A functional linkage perspective

Polycentric urban development has become the buzzword among urban scholars, decision-makers, and planners around the world. From the existing polycentric urban research, a functional approach is increasingly concerned by scholars except for morphological terms. Functional linkages are investigated among the (sub)centers of a polycentric urban system (PUS). However, the (sub)centers are usually pre-defined by a city master plan or identified by a density-sliced approach. However, the definition of the (sub)centers is still dependent on the morphological dimensions rather than functional linkages. To fill the gaps, we proposed a flow-based solution for delineating functional urban regions (FURs). We first built a spatially-embedded network of the entire city within extensive travel flows and then used a community detection method to reveal FURs. The characteristics of the whole PUS and the properties of each FUR are further assessed using complex network analysis. Based on the taxi trajectories of Shanghai, this study shows that the subdivisions of FURs are not necessarily consistent with administrative divisions. The functional linkages are strong among the (sub)centers surrounding the main center, and they are relatively weak among the newly established (sub)centers in the periphery. These findings call for policy interventions to increase the functional linkages of (sub)centers.