Coding Map Information
Numeric, Symbolic, and Color Coding
To be functional to GIS, map information must be organized and segregated by appropriate categories that are specific to each earth resource or human activity. For a particular category to effectively exist in the reality of GIS it must be symbolized by the closest approximation, and then assigned the appropriate "code value."
Coding schemes are the essential component for the clear understanding and appropriate homogeneous delineating of landscape components. Obviously, particular coding schemes lend themselves to particular applications.
Typical GIS coding schemes:
Coding Scheme Examples
The following are the two most basic category listings that characterize the land resources, the water resources, and human activities. This listing is sometimes called Land Cover, Land Type, Land Utilization, Land Activity, and (most commonly) Landuse. To be useful to geographic mapping efforts, all mapped features must be part of a larger classified scheme. For example:
Resource Inventory Land Use and Land Cover
 Agricultural land
 Range land
 Forest land
 Barren land
 Perennial snow or ice
(Level I), Urban Renewal Administration (URA)
 Manufacturing (continued)
 Transportation, communication, and utility
 Cultural, entertainment, and recreational
 Resource production and extraction
 Undeveloped land and water areas
The USGS category  contains the majority of the URA listings  through , and conversely, the URA category  contains the majority listings for the USGS  through .
Needed map information must often be gathered and organized from various sources. Before maps are useful to the Graphic Overlay Method they must be "prepaired." Not all maps are currently available in electronic format. Some information must be prepared by hand.
Here are some useful examples of Value Added Maps.
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