The National Map’s Elevation Point Query Service returns elevations that are interpolated from the 1/3 arc-second 3D Elevation Program (3DEP) DEM dataset. These interpolated point elevations are not official and do not represent precisely measured ground surveyed values.
Elevations derived for a specific location using the Elevation Point Query Service might differ from monumented control elevation values that are published on USGS topographic maps or cited in National Geodetic Survey Marks and Datasheets. Differences between these elevations might exist for features such as mountain peaks or summits, and where the local relief is significant. For most purposes other than engineering, interpolated point elevation values are sufficiently accurate.