Designing zoning systems for flow data

It is now accepted wisdom that the geography used to report census and other spatially aggregated data affects the results to some degree. The modifiable areal unit problem (MAUP) is a fact of life and it is important to discover how best to manage it rather than just ignore it and hope (Openshaw, 1996). One way of managing the MAUP is by designing appropriate small areas for data collection and dissemination. A move in this direction is the reporting of the 2001 UK Census of Population for census output areas based on a carefully and explicitly designed zoning system which will replace the census Enumeration Districts (EDs) as the most detailed spatial unit (Martin, 1998). However, the output areas designed for reporting household and person based data are inherently unsuitable for reporting flow data (journey to work and migration tables). These flow data types also require special data structures in order for the flows to be handled efficiently. In addition, developments in georeferencing technologies create the prospect of increasing levels of geographical precision.