Products from a GIS might be classified in several ways. I will use the terms media, format, purpose, and audience.
Media: I use the term “media” to denote the physical carriers of the information presented to the decision maker. Common media are paper, photographic materials (opaque ones like photographs and translucent ones like slides and films), and electronic visual devices like computer monitors. Three-dimensional electric displays activated by laser beams—called holograms—may be available in the future, but more conventional products are now available that can meet more important, if less exotic, criteria. Almost all products of existing GIS are designed to respond to the sense of vision in some manner.
Format: While the number of visual media that carry information is limited, the number of forms or formats that information can assume is without limit. An (almost) infinite variety can be obtained with characters—the 26 letters of the alphabet, Arabic number symbols, and some special symbols. This type of information is called character-based.
Character-based information can appear in the form of text, tables, lists, formulae, and so on. The way in which information is organized has a tremendous impact on whether or not it will be useful. Character-based information can be processed by an individual in serial fashion (like a reader “processing” this line of text) or in search mode—a procedure in which a person examines unconnected groups of ...