0Geographic Information Systems: A Generic Definition
GIS is a special purpose digital database in which a common spatial coordinate system is the primary means of reference. Comprehensive GIS require a means of:
- Data input, from maps, aerial photos, satellites, surveys, and other sources
- Data storage, retrieval, and query
- Data transformation, analysis, and modeling, including spatial statistics
- Data reporting, such as maps, reports, and plans
Three observations should be made about this definition:
First:- GIS are related to other database applications, but with an important difference. All information in a GIS is linked to a spatial reference. Other databases may contain locational information (such as street addresses, or zip codes), but a GIS database uses geo references as the primary means of storing and accessing information.
Second:- GIS integrates technology. Whereas other technologies might be used only to analyze aerial photographs and satellite images, to create statistical models, or to draft maps, these capabilities are all offered together within a comprehensive GIS.
Third:- GIS, with its array of functions, should be viewed as a process rather than as merely software or hardware. GIS are for making decisions. The way in which data is entered, stored, and analyzed within a GIS must mirror the way information will be used for a specific research or decision making task. To see GIS as merely a software or hardware system is to miss the crucial role it can play in a comprehensive decision making process.
The GIS View of the World
GIS provide powerful tools for addressing geographical and environmental issues. Consider the schematic diagram below. Imagine that the GIS allows us to arrange information about a given region or city as a set of maps with each map displaying information about one characteristic of the region. In the case below, a set of maps that will be helpful for urban transportation planning have been gathered. Each of these separate thematic maps is referred to as a layer, coverage, or level. And each layer has been carefully overlaid on the others so that every location is precisely matched to its corresponding locations on all the other maps. The bottom layer of this diagram is the most important, for it represents the grid of a locational reference system (such as latitude
and longitude) to which all the maps have been precisely registered.
Application Areas
One of the first major areas of application was in natural resources management, including management of
wildlife habitat, wild and scenic rivers, recreation resources, floodplains, wetlands, agricultural lands, aquifers, forests.
One of the largest areas of application has been in facilities management. Uses for GIS in this area have included
- locating underground pipes and cables,
- balancing loads in electrical networks,
- planning facility maintenance,
- tracking energy use.
