Areas studied in geography, such as states, counties, census areas, or enumeration districts, which may be arbitrary units unconnected with any existing spatial patterns developed—the boundaries of many African states, for example, cut across cultural and ethnic regions. In many cases the investigator has to use the units for which data are available rather than the units which are more suited to the investigation. Guo and Bhat (2004) Transportation Res. Record 1898 contend that the fundamental issue is the inconsistency between the analyst’s definition of areal units, and the decision-maker’s perception of residential neighbourhoods, and propose a way out of the problem.