The influence of the impedance function on gravity-based pedestrian accessibility measures: A comparative analysis

Pedestrian accessibility has been growing in importance as an urban planning objective. Assessing it with gravity-based or potential accessibility measures requires the selection of an impedance function in order to reflect the friction of distance. The choice of impedance function is crucial to pedestrian accessibility assessment due to the level of spatial data detail required and also because perceived distances differ from physical distances. Here, we measure and compare 20 gravity-based measures, varying the impedance function and associated parameters. Correlation analysis revealed a significant and strong correlation between the measures. Factor analysis extracted two groups of measures, differing mainly in their maximum cutoff travel distance, i.e. the distance at which the impedance function reaches zero. Spatial analysis revealed that all measures produce similar spatial results in terms of identifying high and low accessibility locations but different values for medium accessibility locations. Places located at between 200 and 400 m from an opportunity are especially sensitive to the impedance function used. We promote a cumulative–Gaussian approach to measure pedestrian accessibility, as it explicitly includes the travel tolerance concept and we found it to be the most robust measure in terms of data variability.

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