Unifying Access

Abstract

Since Hansen’s seminal 1959 paper, measures of access have evolved with technology and through practical applications. The myriad of distinct but familially related access measures created many more options to measure places, but has sown needless confusion. This paper systematically reviews measures of access across disciplines. We categorize measures of access, covering both mainstream and innovative but less widely-used techniques; each access measure (topological, contiguous, cumulative opportunities, utility, flow-based measures) is separated into Primal and Dual measure, based on whether accessibility is represented by the level of reachable opportunities or by the travel impedance. We show access measures are unified by the same intrinsic structure consisting of travel impedance and the opportunities reachable, and that access measured by different methods are equivalent under specific assumptions on travel impedance, and the accounting of relevant opportunities. This paper overviews the use of access measures from the existing literature, and clarifies measures of access, which should help users in the selection and appropriate use of access measures for the relevant context.