A GIS is a Geographic Information System. Basically, it's a map on steroids. Data is specifically tagged to location allowing very complex mapping and analysis, layer by layer. A layer of water features can interact with a layer of municipal services or lot lines or underground petrol tanks or vegetation cover – all of which allows true spatial analysis of interacting data points or phenomena.
We can look back to the start of GIS mapping in 1854, when London physician John Snow plotted cholera deaths on a London map with water pumps, allowing him to pinpoint the pump causing the disease outbreak. This first GIS map was also the beginning of the study of Epidemiology and extended the concepts behind the Germ Theory of Disease.
The first computerized GIS was undertaken in Canada by Roger Tomlinson who, in 1963, using the most basic of computers, created a cross-country inventory of natural resources. GIS today is found in every area of business, government, and non-governmental agencies. Route optimization; water mains location; search and rescue; disease outbreaks; charting changes to our natural world — all of this is done with GIS.
Getting Started in GIS
Introduction to GIS
What you can do with GIS
Ordnance Survey (OS) 2:40