Urban Nodal Regions Through Communities of Functionally Critical Locations in the Transportation Network

Abstract

The ease of mobility across the urban environment is known to be a major factor of the spatial organization of the city. It is commonplace to look at accessibility in this space as a structuring element of urban functional areas. In this tradition, the urban space is segmented into nodal regions or communities on the basis of trip origins and destinations recorded to uniformly sized grid cells or Voronoi polygons. However, this approach ignores the role of the layout of the transportation network in forming the regionalization of the urban structure. In this article, we argue that an effective approach to identify socioeconomic communities in an urban area is by means of its functionally critical elements. The proposed approach starts with the identification of functionally critical nodal points in the city’s transportation system, which allow us to capture people’s activity spaces on the aggregate. Then we construct a weighted directed graph based on these functionally critical locations, where each node in the graph denotes a functionally critical location and each edge denotes the presence of travel trajectories between pairs of critical locations; the weight of edges denotes the travel intensity. We introduce recent methods of network science to identify the socioeconomic communities of the urban region, and we examine and discuss interesting socioeconomic clusters. As a use case, we use a big data set that contains all the trajectories of over 11,000 taxis over a month in Wuhan, China. The results of the analysis suggest that (1) characteristics of socioeconomic clusters are very different from the administrative subdivisions of the city of Wuhan; (2) compared to regionalizations that account only for trip ends, the functional criticality approach provides us better ways to understand the regionalization structure of a city, especially how activity spaces are shaped by civil infrastructures such as bridges across major waterways; and (3) the functional criticality approach enhances urban communities outlined solely on the basis of physical transportation network topologies.