Geographic data is derived from a variety of sources: satellite imagery,
airphotos, ground surveys, and tabular data. Use of tabular data, census
data as an example, may also be incorporated into a GIS. Information found
on topologic maps must be converted to a digital form recognized by the
computer to be incorporated into the GIS database.
The digitizing process usually requires either a pointer and digitizing table, or a scanner. As the features are outlined by the pointer, the operator also records the type of feature and any supplementary information necessary to describe that feature. In the case of a scanned image, the features, once they are read into digital format, are singled out and labeled appropriately.
Storage and manipulation of the geographic data, unless unusually large, are typically handled in a PC or network environment.
Displayed data can take the form of a printed image (usually produced by a plotter, or color printer) or a screen image. More sophisticated GIS packages offer the ability to create three dimensional displays.
Software applications are selected based on the user's needs. All GIS packages perform similar generic functions: encode, store, retrieve, manipulate, and analyze. Variations between packages arise in the ability to handle raster or vector data, processing capabilities, and display options.
eqpmnt.html
Institute of Water Research, Michigan
State University
Last Revision: February 22, 1997