Trends and Issues in Accessibility Studies in the GIS Era

Abstract

Various studies have been conducted on accessibility in the field of geography. Diverse accessibility concepts were used in those studies and many methods for measurement have been developed. Improved models of existing accessibility continued to be contrived, which made accessibility concepts complex.
This paper has two purposes. First, the author classifies the quantitative measurement methods for accessibility and points out the features and problems of each model. The second aim is to investigate the changes in accessibility studies with advances in geographical information systems (GIS).
The themes of accessibility that have attracted the most attention are transportation, spatial equity in service, and living behavior of residents. Quantitative accessibility is composed of relative accessibility and integral accessibility, in particular the latter has been mainly used for a long time. It is considered that the most useful measures of accessibility are the gravity-model measure and cumulative-opportunity measure. However, it has been pointed out that these measures of integral accessibility include some problems.
GIS provide very useful functions for measuring accessibility. One is a tool for determining the shortest path in a network, and the other is a tool for spatial analysis such as buffering and overlay. Due to the drastic reduction in the time required for measuring accessibility, the trend in accessibility studies has changed markedly. Precise studies using large amounts of data have increased, and new accessibility measures based on the concept of time geography have been established.
In contrast with integral accessibility, “place accessibility, ” the new space-time measure, “individual accessibility, ” has been introduced. The latter enables to measure the accessibility by individuals. The space-time constraints in individual and multiple-stop trips are taken into consideration in the space-time measure, so that the problems of integral accessibility are overcome. However, the space-time measure has some problems not seen in integral accessibility. Further improvements will continue to be made, and analysts must choose which measure to use according to the purpose of analysis.