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How accurate is the elevation data in the Geographic Names Information System Database? How was it measured?

The elevation figures in the Geographic Names Information System (GNIS) are not official and do not represent precisely measured or surveyed values. Only the geographic name and locative attributes are official.

Elevations are derived from data in The National Map. The data are interpolated from seamless raster elevation models for the given coordinates and might differ from elevations cited in other sources, including those published on USGS topographic maps. Published map data represent precisely surveyed points that often are marked by a benchmark or triangle on the map and a benchmark seal physically anchored into the ground at the site.

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