(Data West Research Agency definition: see
GIS glossary.) A GIS can be distinguished by listing the types of questions it can (or should be able to) answer as opposed to being described: a) through formal definitions, and b) through its ability to carry out spatial operations, and linking data sets together with location as the common key. There are five generic questions that a sophisticated GIS can answer:
1 - Location What is at ...? The first of these questions seeks to find out what exists at a particular location described in various ways (e.g., place name, post or zip code, or geographic references).
2 - Situation/Condition Where does it exist? The second question is the converse of the first and requires spatial analysis to answer. Instead of identifying what exists at a given location, a location is found where certain conditions are satisfied (e.g., an unforested section of land of at least 2000 square meters in size, within 100 meters of a road, and with soils suitable for supporting buildings).
3 - Trends What has changed since...? The third question involves both of the first two, and seeks to find the differences within an area over time.
4 - Patterns What spatial patterns exist? The fourth question is more sophisticated; the question is asked to determine whether cancer is a major cause of death among residents near a nuclear power station or how many anomalies there are that don't fit a predetermined pattern and where they are located.
5 - Modeling What if...? The fifth question is posed to determine what happens, for example, if a new road is added to a network, or if a toxic substance seeps into the local groundwater supply. (Answering this type of question requires both geographic as well as other information, and possibly scientific laws.)