Digitized data is layered, and these layers are combined to construct constraint maps that then can be subjectively analyzed as to the best alternative. Ability to form a logical sequence. The process of cartographic modeling is characterized by working backward through the process to insure that all data that will be needed are identified. Data that will not be used therefore will not be collected. This backward procedure insures that any judgments to be made are explicitly identified.
Subjective judgments are an integral feature of cartographic modeling.
Contiguity measures evaluate characteristics of spatial units that are connected. These units share one or more characteristics with adjacent units and form a group. Contiguity is used to measure shortest and longest straight line distances across and area and to identify areas of terrain with specified size and shape characteristics. An area of continuous pastureland with an area of no more than 10 acres with no part of it wider than the sound of the Acme Pig Call can be heard. The simple distance between features, commonly units of length but can be other units such as how far away the ACME PIG CALL can be heard.