Choosing a Map Projection

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Map Projection Uses in a GIS

Select a map projection for the GIS database to (Maling, 1992):

  • decide how to best display the area of interest or illustrate the results of analysis
  • register all imagery to a single coordinate system for easier comparisons
  • test the accuracy of the information and perform measurements on the data

Deciding Factors

Depending on your applications and the uses for the maps created, one or several map projections may be used. Many factors must be weighed when selecting a projection, including:

  • type of map
  • special properties that must be preserved
  • types of data to be mapped
  • map accuracy
  • scale

If you are mapping a relatively small area, virtually any map projection is acceptable. In mapping large areas (entire countries, continents, and the world), the choice of map projection becomes more critical. In small areas, the amount of distortion in a particular projection is barely, if at all, noticeable. In large areas, there may be little or no distortion in the center of the map, but distortion increases outward toward the edges of the map.

Guidelines

Since the sixteenth century, there have been three fundamental rules regarding map projection use (Maling, 1992):

  • if the country to be mapped lies in the tropics, use a cylindrical projection
  • if the country to be mapped lies in the temperate latitudes, use a conical projection
  • if the map is required to show one of the polar regions, use an azimuthal projection

These rules are no longer held so strongly. There are too many factors to consider in map projection selection for broad generalizations to be effective today. The purpose of a particular map and the merits of the individual projections must be examined before an educated choice can be made. However, there are some guidelines that may help you select a projection (Pearson, 1990):

  • Statistical data should be displayed using an equal area projection to maintain proper proportions (although shape may be sacrificed).
  • Equal area projections are well-suited to thematic data.
  • Where shape is important, use a conformal projection.