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What is the difference between:

  • a map that has a projected coordinate system of WGS_1984_UTM_33N, a geographic coordinate system of GCS_WGS_1984, and a datum of D_WGS_1984
  • a map that has no projected coordinate system, but with the same geographic coordinate system of GCS_WGS_1984, and the same datum of D_WGS_1984
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The first (WGS 1984 UTM 33 North) has map units of meters, while the second has decimal degrees. If you're talking about a two-dimensional display, the WGS 1984 (decimal degree) data is often displayed using a "pseudo-Plate Carrée" projection. That is, the decimal degrees are treated as if they're linear units and the features are just displayed. A standard Plate Carrée projection would convert the degrees to radians and then multiply by the semimajor axis or radius of the geographic coordinate reference system.

Depending on software and whether data is in a projected or geographic coordinate reference system, there may be different functions available. For instance, in ArcMap, the Measure Tool can provide planar (projected) or geodesic-based distances if the data frame (map) coordinate reference system is projected.

  • Thank you. Does this mean that technically the WGS84 (decimal degree) has lesser accuracy because of the degree conversion involved? – Geoniette Apr 29 '15 at 17:36
  • You mean when converting to meters to calculate a distance for instance? No, not inherently less accurate. – mkennedy Apr 29 '15 at 21:24

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