The preceding discussion leads me to revise my working definition:
As I mentioned earlier, a geographer named David Cowen defined GIS as a decision-support tool that combines the capabilities of a relational database management system with the capabilities of a mapping system (1988). Cowen cited an earlier study by William Carstensen (1986), who sought to establish criteria by which local governments might choose among competing GIS products. Carstensen chose site selection as an example of the kind of complex task that many organizations seek to accomplish with GIS. Given the necessary database, he advised local governments to expect that a fully functional GIS should be able to identify property parcels that are:
- at least five acres in size;
- vacant or for sale;
- zoned commercial;
- not subject to flooding;
- located not more than one mile from a heavy duty road; and
- situated on terrain whose maximum slope is less than ten percent.
The first criterion-identifying parcels five acres or more in size-might require two operations. As described earlier, a mapping system ought to be able to calculate automatically the area of a parcel. Once the area is calculated and added as a new attribute into the database, an ordinary database query could produce a list of parcels that satisfy the size criterion. The parcels on the list might also be highlighted on a map, as in Figure 1.11.1, below.
Figure 1.11.1 The cartographic result of a database query identifying all property parcels greater than or equal to five acres in size. (City of Ontario, CA, GIS Department. Used by permission.)
The ownership status of individual parcels would be an attribute of a property database maintained by a local tax assessor's office. Parcels whose ownership status attribute value matched the criteria "vacant" or "for sale" could be identified through another ordinary database query.
Figure 1.11.2 The cartographic result of a spatial intersection (or map overlay) operation identifying all property parcels zoned for commercial (C-1) development. (City of Ontario, CA, GIS Department. Used by permission.)
Center (DTSTC) Technology (DTS) Toxic Substances Transportation (Caltrans) Veterans Affairs (CalVets) Water Resources o de Vehiculos Motorizados Digital Library Disabled Veteran Business Enterprise Certification Program Apprenticeship St Codes St Communicable Disease Engineering Environmental Occupational Disease Gambling Housing Policy Labor St Enforcement Labor Statistics Research L Right Way L Resource Law Enforcement General Library Measurement St Mines Geolo