All maps have some particular purpose(s) or raison d'etre. A primary use is just to record what is there; another is to aid a person in locating oneself by observing position relative to identifiable surroundings. But, a third involves interrelating the information in maps to a specific need or analysis which will lead to assessment of site suitability for development or other types of decision-driven actions. Thus, if the task is to select a place in which to build a factory to produce metal products, then a large amount of information, much of it being location-dependent and therefore mappable, must be gathered and integrated. This list, while incomplete, shows the diversity of data elements (themes or attributes) required:

Often, a list may grow to 50 or more major factors that must be considered in the planning stage or at other points in the decision-making process. Along with maps addressing these data elements, other types of input include tabular summaries, statistical analyses, graphical plots, and timely remote sensing imagery including classifications.

Or, the challenge may be to select within a region some favorable area to grow one or more cash crops on a large scale. In addition to some of the factors in the above list, these elements also are especially pertinent:

In this case, something more is needed. To operate an enterprise prone to the vicissitudes of climate, economics, and public tastes it is necessary to have some understanding of how the factors, as variables, interact in the continuing process of production. What changes in fertilizing are demanded when a farm has been dedicated to perhaps one crop over a long period? How much water must be diverted during a drought? Should some farms be reallocated to other crop types in response to long-term market trends? Are regulations imposed by federal, state, and local governments being met or violated?

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