TRANSACTIONSOFTHEROYAL SOCIETYOFTROPICALMEDICINEANDHYGIENE(1996)90,337-339 337 ileading Article1

tion started in the mid 1980s and has since snread to all countries of the world. A GIS is a comput&software package that is concerned with the capture, storage, man-ipulation, query, display and analysis of any and all types of geographical information, (BLJRROUGH, 1986; CHORLEY, 1987; LAURINI & THOMPSON, 1992; ESRI, 1993). There are now many different GIS packages avail-able throughout the world. The unique attraction of GIS is that it adds a geographical dimension to information held in computer systems that previously lacked it or was stored using database software which was inade-quate to handle and manipulate the geography associ-ated with the data. Traditional geographical information consists of vir-tually everything shown on maps of any kind; for exam