The operationalization of basic time-geography concepts on street networks and their validity

Abstract

The time-space measure of accessibility based on the time-space path (TSP) and the potential path area (PPA) in time-geography is a powerful framework for the analysis of human behavior and accessibility patterns at the micro-scale. However, the reality of the TSP and the PPA on continuous space is low, although their geometric manipulation is easy. One possible means of raising the reality of the TSP and the PPA is to define the space to be analyzed as a street network which takes actual activity locations and the travel environment into account. A technical constraint related to the operation of the TSP and the PPA on a street network was difficult resulting from the large volume of spatial data, although the utilization of geographical information systems (GIS) has recently solved this constraint. This article has two purposes: (1) to describe a method for operating the TSP and the PPA on a street network using GIS, which is indispensable for accessibility measurement using time-space measures, and (2) to compare the results of measuring time-space accessibility on continuous space and a street network in order to determine the validity of the latter. The operation of the TSP and the PPA is performed using the following procedures: (1) construct a street network that consists of links and nodes with temporal impedance on a GIS environment; (2) operate the TSP by using the shortest path search function, which is a basic network analytical method of GIS; (3) operate the PPA by using the allocation method, which searches links and/or nodes located at a specific distance from the cardinal node(s). The comparison of the PPA on continuous space and on a street network reveals that the smallest range of the PPA on the latter is half that of the former and its dispersion is wider. Moreover, the shape of the PPA on a street network is not close to a circle in terms of the form ratio. The breadth and shape of the PPA on the network depend on the existence of barriers for rectilinear travel such as a broad road, railway, stair and open space that do not permit the passage of the general public, as well as the shape of city blocks. The PPA on continuous space, however, cannot take into account these factors. The above-mentioned results demonstrate the higher reality of the PPA on a street network in a quantitative sense.