In a planar coordinate system, three coordinates that locate a point by its distance from an origin (0,0,0) where three orthogonal axes cross. Usually, the x-coordinate is measured along the east–west axis, the y-coordinate is measured along the north–south axis, and the z-coordinate measures height or elevation.

http://support.esri.com/en/knowledgebase/GISDictionary/term/x%2Cy%2Cz%20coordinates

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