So far, a GIS has been described in two ways: 1) through formal definitions, and 2) through its ability to carry out spatial operations, linking data sets using location as the common key. You can, however, also distinguish a GIS by listing the types of questions it can (or should be able to) answer. For any application there are five generic questions that a sophisticated GIS can answer.
Location what is at..?
The first of these questions seeks to find out what exists at a particular location. A location can be described in many ways using, for example, a place name, a post or zip code, or a geographic reference, such as latitude and longitude.
Condition where is it?
The second question is the converse of the first and requires spatial analysis is to answer. Instead of identifying what exists at a given location, you want to find a location where certain conditions are satisfied (e.g., an unforested section of land at least 2,000 square meters in size, within 100 meters of a road, and with soils suitable for supporting buildings).
Trends what has changed since...?
The third question might involve both of the first two and seeks to find the differences within an area over time.
Patterns what spatial patterns exist?
This question is more sophisticated. You might ask this question to determine whether cancer is a major cause of death among residents near a nuclear power station. Just as important, you might want to know how many anomalies there are that don't tit the pattern and where they are located.
Modeling What if. .. ?
"What if ...” questions are 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 geographic as well as other information.
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