Data Standards - Projection
 

A map projection is a mathematical model for conversion of locations from a three-dimensional earth surface to a two-dimensional map representation. This conversion necessarily distorts some aspect of the earth's surface, such as area, shape, distance, or direction. Projection types are based on the geometric form used in the transfer from the spherical earth to a flat surface.

  • Azimuthal (or Planar)
  • Conic
  • Cylindrical
  • Pseudocylindrical or Compromise Projections

Fiigure 2: Planar, Conic and Clylindrical projections.

Different types of projections are used for specific areas of the Earth and minimize the distortions for that part of the globe. Some of these projections include Mercator, Robinson, Transverse Mercator, Eckert, and Lambert Conformal Conic.



Map projections are very important when more than one data source is used. For example, if a base map is in the Mercator projection and a data set of cities is in the Robinson projection, the cities will not be displayed in the correct location relative to the base map.

Figure 3: Animated Illustration of projection distortion (SIC 2002)

 

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