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This page is mainly concerned with calling out the types of maps and attributes, and other data sources used in a GIS application.

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 a position relative to identifiable surroundings. But, a third purpose involves interrelating the information in maps to a specific need or analysis, which leads 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 we must gather and integrate a large amount of information that depends on location and is, therefore, mappable. This list, while incomplete, shows the diversity of data elements (themes or attributes):

Topgraphic Relief
Slope Stability
Bearing Strength of Soils
Ease of Excavation
Extent of Forest Cover
Availability of Water
Land Ownership
Current Costs of Available Land
Zoning Laws
Present Highway Locations
Proximity to Railroads
Access to Power Lines
Existing Buildings
EPA Requirements
Direction of Prevailing Winds
Proximity to Housing
Cost of Living
Tax Rates

Often, a list may grow to fifty or more major factors that we must consider 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 that includes 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, the following elements also are especially pertinent:

Soil Types
Soil Moisture
Seasonal Rainfall
Flooding Potential/Frequency
Depth to Groundwater and Supply Rates
Other Sources of Water
Number of Sunny Days
Frost Dates
Distribution of Existing Farms
History of Crop Productivity
Cost of Fertilizer
Insect Infestation Control
Seasonal Market Conditions

In this case, we need something more. 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 production process. What changes in fertilizing are demanded when a farm has been dedicated to 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?

15-4: Suppose you are given the task of making the preliminary assessment of the feasibility of constructing a steel plant. Think of as many factors, for which maps or data are to be sought, as you can that bear on determining where the plant should be located. ANSWER

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Primary Author: Nicholas M. Short, Sr. email: [email protected]