The National Map (USGS)The Elevation Point Query Service returns the elevation in international feet or meters for a specific latitude/longitude (NAD 1983) point from the USGS 3DEP 1/3 arc-second layer hosted at the NGTOC. If unable to find data at the requested point, this service returns -1000000. Input parameters: x (longitude), y (latitude), units (Feet, Meters), output (XML, JSON). Latitude and longitude must be specified in decimal degrees with southern latitudes and western longitudes represented as negative values. The 1/3 arc-second dataset covers nearly all the U.S. states and territories, though Alaska has only partial coverage.