Geographic Information Systems

2 Pages 382 Words

Geographic Information Systems
Geographic information systems (GISs) provide the capability to view the topology of a landscape, including features such as roads, sewers, electrical cables, and mineral and soil content. GIS is a technology that has promised much and finally is beginning to deliver. As with the expert systems technology, GISs are truly useful when they integrate with the business process. From a technological perspective, GISs must operate on standard technologies, integrate with the organization SDE, and directly access the organizational databases.
Conceptually, GISs enable users to store virtually unlimited geographic information as a series of layers. Some layers, such as street layouts, compose the base map. Other layers, such as wetlands and subterranean water sources, are thematic layers that serve a specific, sometimes narrow purpose. A GIS user can custom design a printed map to fill a particular need by simply selecting the relevant layers. Selecting the street layer and the wetlands layer would produce a map of wetlands and their relationship to the streets. Selecting the subterranean water sources layer and the wetlands layer would show the wetlands superimposed on the features of the underlying aquifer.
Each line, curve, and symbol in a map is fixed in space by a series of numbers, called the spatial data. Spatial data describes the precise positioning of map objects in three-dimensional space.
Besides storing map objects such as street segments and wetland boundaries, GISs enable designers to specify attributes the users want to associate with any map object. Such attributes may be descriptive data, detailed measurements of any kind, dates, legal verbiage, or other comments. When viewing a map on-screen, the user can click any map object, and a data-entry window will open to display the attributes associated with that object. Attribute information is usually stored in RDBMS tables, and each map laye...