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Why do all of the coordinates (latitude and longitude) in the Geographic Names Information System seem incorrect?

Coordinates that seem to be incorrect in the Geographic Names Information System might just be projected on a different datum from the datum used on your map or your positioning system (GPS).

 Most USGS maps published approximately 1940-1995 are projected on the North American Datum of 1927 (NAD27). Later maps are projected on the North American Datum of 1983 (NAD83). The "datum shift" changes the coordinate values of fixed ground points.

The shift is different for different coordinate systems. UTM, State Plane, and geographic (latitude/longitude) values change by different amounts. A change in UTM values of roughly 200 meters in the north-south direction (the exact value varies with location) indicates a NAD27-NAD83 datum shift. Changes in State Plane Coordinate System (SPCS) values can be much larger, and can vary between states.

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