More than a century ago, epidemiologists and other medical scientists began to explore the potential of maps for understanding the spatial dynamics of disease. A study carried out by John Snow is often cited to show that the importance of spatial dynamics in the understanding of disease, and the use of maps to describe and analyze it, is not so recent. Dr Snow made the hypothesis that cholera might be spread by infected water supplies more than a century ago, using maps to demonstrate in a striking fashion the spatial correlation between cholera deaths and contaminated water supplies in the area of Soho in 1854. Scholten and Lepper use the example of AIDS, stressing the importance of the spatial distribution of the disease, which they say has been too often overlooked. Modelling the spatial distribution of AIDS can contribute to both educational intervention and the planning of health care delivery systems.
Mapping can play an important role in both areas as it is an excellent means of communication.
In order to be of use to resource planners, predictions of AIDS should include a spatial component. The database is central to the GIS and contains two main types of data. The information contained in the spatial database is held in the form of digital coordinates, which describe the spatial features. Normally, the different sets of data will be held as separate layers, which can be combined in a number of different ways for analysis or map production. The Digitizing System One important source of locational data is existing paper maps, for example, road maps or administrative boundaries maps.