A GIS is an analytical tool that allows the understanding of how one map feature is related to another, in space. It is not simply a cartographic tool -- although it can, given the order, create maps in different scales, in different projections and in different colours.

To go beyond just making pretty pictures, it is essential to have 3 pieces of information about every feature stored in the computer: what the feature is, where it is located and how it relates to other features -- for instance, which roads link to form a network and where. The GIS does that for you.

Depending on what one wants to see on the map, it can combine 2 or more maps displaying vastly different information into a single map. For instance, it can put on one map the population of each village in a district and their respective annual incomes by "intelligently" superimposing the individual maps of the 2 variables.

Likewise, it can create a stack of many such layers of maps and compress it into a single display. But the increasing "trees" of information have to be constantly chopped down -- since layers of ever-increasing and mind-overloading data are classified into categories -- to keep the woods in sight.

This is the analytical side of GIS, which requires knowledge of advanced statistical techniques. It enables those who have no formal training in painstaking cartography to make maps and models. Its jazzy graphics allow you to see, analyse, and anticipate the effects of a certain happening on the general course of events, even, say, the effect of a forest-fire on the life of animals.