A wide range of datasets on the locations where work, education, shopping, health, and leisure facilities are available are now held on GIS databases in most local authority areas. Data on employment by market sector and postcode can be purchased cheaply from commercial data suppliers and there is a growing portfolio of national data covering shopping, health and other opportunities (see Section 17.2).
Often work, shopping and other opportunities are situated in local centres allowing the analysis to be simplified. The accuracy of the analysis can be improved by using measures of activity where possible. For example the existence of a hospital or college does not describe what treatments or training courses are available or how large the centre is, so using number of treatments, consultations, courses etc. within the analysis is more useful.
One of the strengths of accessibility analysis is that it can look at minority groups or specific trip purposes. Aggregation of results can easily obscure the primary benefits of undertaking the analysis, i.e. to investigate the distribution of benefits. To avoid these problems, map based presentation is a powerful way to show the distribution of impacts and highlight locations with poor public transport provision for particular trip purposes. However it is also sometimes helpful to have a single or limited range of summary indicators which can be incorporated in the AST. In these circumstances ratios can be particularly helpful at comparing the overall impacts of changes on, for example, unemployed people when compared with the population as a whole (see Table 11.4).
