About Geographic Coordinates Collection by Stefan A. Voser

MapRef

8. October 1998

Table of Content

1. Notes
2. Terminology confusion with geographic coordinates
3. Others

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Notes

• Geographic co-ordinates are not planar coordinates!
• Geographic co-ordinates are based on a specific reference System. (e.g. sphere or ellipsoid).
• Geographic co-ordinates define the perpendicular direction on the surface of the reference system
• Geographic co-ordinates are ambiguous!
• Geographic co-ordinates may define different points on the earth's surface. This depends on their reference system. (the geodetic datum problem).
• One point on the earth's surface may have many geographic co-ordinates, depending on their reference system (geodetic Datum). 
• Changing Geographic Coordinates means:
• Map Projection

Transformation from the curved surface to a plane. 
• Geodetic Datum Transformation

Changing geographic coordinates between different reference systems or reference surfaces.

Terminology confusion with geographic coordinates

• astronomical coordinates

physically defined perpendicular, based on the gravity
• geodetic coordinates

mathematically defined perpendicular, based on the reference surface, specifically ellipsoid , used for large and medium scale mapping, and in geodesy. 
• geographic coordinates

mathematically defined perpendicular, based on the reference surface, typically spheres, used for small scale mapping

Others

• Theory
• Frequently Asked Questions