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Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition by Michael D. Kennedy

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Geographic vs. Projected Coordinates: A Comparison

  • Advantages of the spherical coordinate system—You can represent any point on the Earth’s surface as accurately as your measurement techniques allow. The system itself does not introduce errors.
  • Disadvantages of a spherical coordinate system—You will encounter complex and time-consuming arithmetic calculations in determining the distance between two points or the area surrounded by a polygon determined by a set of points. Latitude-longitude numbers plotted directly on paper in a Cartesian coordinate system result in distorted—sometimes greatly distorted—figures.
  • Advantages of a projected coordinate system on the Cartesian plane—Calculations of distances between points are trivial. Calculations of areas are relatively easy. Graphic representations are realistic, provided the area covered is not too large.
  • Disadvantages of a projected coordinate system on the Cartesian plane—Almost every point is in the wrong place, although maybe not by much. All projections introduce errors. Depending on the projection, these errors are in distances, sizes, shapes, or directions.

Whether you use geographic or projected coordinates, ensuring that the parameters of geographic data match is of paramount importance in combining GIS data sets if you want the right answers!13

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