Analysing or interpreting the links between environment and health is, by its very nature, a spatial problem. Levels of risk vary geographically in response to variations in environmental conditions; health outcome and associated levels of need and health support vary as a consequence. Many of the questions facing the environmental epidemiologist and policy-maker are thus inherently geographical, and spatial analysis and mapping are vital components of their work. In research terms, these techniques provide an important step in the formulation and testing of hypotheses about links between environment and health. In policy terms, they are a valuable means of directing policy to areas and problems of greatest need, and of monitoring policy performance and effects.
Spatial analysis and mapping in environmental health have a long history. It is now traditional to trace their origin back at least as far as the seminal study of John Snow on cholera in London (Snow, 1855). Until recently, they could only be carried out manually, or using relatively simple mapping packages. Over the last ten years, however, the capability for spatial data manipulation has been revolutionised by the development of GIS. These systems have made mapping and many spatial analytical techniques much more readily available and enabled data visualisation in map form. They have also stimulated a wide range of new research initiatives into spatial operations and concepts which have greatly advanced understanding of how to analyse and interpret spatial phenomena.
Geographical information systems can simply be described as systems for the collection, storage, manipulation and display of spatially-referenced data (Maguire et al., 1991). As such they perform a wide range of different functions. In addition to data capture and cleaning, data integration and data search and retrieval, these features include:
*This chapter was prepared by D. Briggs and K. Field