Accessibility and Spatial Interaction
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Accessibility and Spatial Interaction

Edited by Ana Condeço-Melhorado, Aura Reggiani and Javier Gutiérrez

The concept of accessibility is linked to the level of opportunities available for spatial interaction (flows of people, goods or information) between a set of locations, through a physical and/or digital transport infrastructure network. Accessibility has proved to be a crucial tool for understanding the framework of sustainability policy in light of best practice planning and decision-making processes. Methods such as cost–benefit analysis, multi-criteria analysis and risk analysis can benefit greatly from embedding accessibility results. This book presents a cohesive collection of recent studies, modeling and discussing spatial interaction by means of accessibility indicators
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Chapter 4: High resolution accessibility computations

Thomas W. Nicolai and Kai Nagel


Accessibility is a concept which either looks at how easy it is to reach a certain location from many other locations, or how easy it is to reach other locations or opportunities from a given starting point. This chapter looks at the latter, discussing that this is a quantity that can be defined separately for every point (x,y) in space, rather than treating accessibility as uniform within, say, zones. As a result, accessibility can also be seen as a continuous field A(x,y) in the two-dimensional environment. The chapter then continues to discuss how A(x,y) can be efficiently computed for regional scenarios. The approach combines interpolation of values computed on a grid with fast shortest-path tree computations and information caching for repeated sub-computations of the same quantities, using the econometric logsum term as an example of a possible indicator of accessibility. A Zurich scenario needs about two minutes of computing time on a regular desktop computer in order to compute A(x,y) at a resolution of 100 m x 100 m. As a sensitivity study, workplace accessibility maps are given for free speed car, congested car, bicycle and walking. One can for example observe that accessibility by bicycle is similar to congested car accessibility within the urban area, while it is worse outside and considerably worse when compared to free speed car transport. Similarly, walking accessibility is similar to bicycle and congested car transport in the innermost urban core, but considerably worse everywhere else.

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