Examples of measures of accessibility. Terms: accessibility, activity space, buffer, centroid (geometric within an administrative unit), network distance. This figure demonstrates the different approaches to measuring boundaries of spatial units used for accessibility measures such as density. Firstly, the point from which the measures will be taken is defined; in this case a geometric centroid of an administrative unit (census collector district, the smallest administrative spatial unit in Australia) is calculated. From this point, two buffers are drawn; the first using Euclidean (straight-line) distance and the other using network distance. The third spatial unit relates to activity space. This relates to an individual's travel patterns over a course of a day with the destinations visited and the travel routes mapped (both of which can be captured using a Global Position System (GPS) device). A buffer is also placed around these to capture exposures nearby to the visited locations and also nearby to their household (represented by the geometric centroid).
Thornton et al. International Journal of Behavioral Nutrition and Physical Activity 2011 8:71 doi:10.1186/1479-5868-8-71