Coordinate system.docx - Geographic Coordinate System A geographic coordinate system(GCS uses a three dimensional spherical surface to define locations

# Coordinate system.docx - Geographic Coordinate System A...

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Geographic Coordinate System A geographic coordinate system (GCS) uses a three dimensional spherical surface to define locations on the earth. A GCS is often incorrectly called datum, but datum is only one part of a GCS. A GCS includes an angular unit of measure, a prime meridian, and a datum (based on a spheroid). A point is referenced by its longitude and latitude values. Longitude and latitude are angles measured from the earth's center to the point on the earth's surface. The angles often are measured in degree (or in grads). The following illustration shows the word as a globe with longitude and latitude values. In the spherical system, horizontal lines, or east-west lines, are lines of equal latitude, or parallels. Vertical lines, or north-south, are lines of equal longitude, or meridians. These lines encompass the globe and form a gridded network called graticule. The line of latitude midway between the poles is called the equator. It defines the line of zero latitude.