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Open Access Publications from the University of California

Measuring Physical Accessibility with Space-Time Prisms in a GIS: A Case Study of Access to Health-Care Facilities

  • Author(s): Lee, Ming S.;
  • McNally, Michael G.
  • et al.

Physical accessibility is a measurement of opportunities available to people in a geographical region. The purpose of such a measurement is for the redirection of regional and transportation policies toward the provision of quality of life. Public policies should provide individuals with more options to choose from, and these options should be more equally distributed among the population. A physical accessibility measure can reflect the efficiency of policies in addressing these issues. This paper presents a framework that implements the concept of space-time prisms in a Geographic Information System (GIS) for measurement of physical accessibility. The novelty of the framework is in its use of information technologies and its strength is in the ease of implementation. The analytical procedure begins with preparation of databases. An algorithm operating with a GIS is developed to define feasible opportunities within various space-time prisms by allowing spatial and temporal constraints to vary. While this enables the modeling of individual accessibility, it can also be applied to measure the traditional zonal measures. A case study utilizing data from Portland, Oregon illustrates the processes of database preparation and measurement of zonal accessibility. A hypothetical example demonstrates how individual accessibility can be measured by the proposed approach.

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