North American Datum 1927. It is broken down into different areas, from Central America to Greenland. Yes I know Central America is not in North America, but I don't make this stuff up.

North American Datum 1927, CONUS - Also called NAS-C (or sometimes just NAS), this datum is being superceded by NAD83 and WGS84, but is still very commonly found used for USGS 1:24000 DRGs and DEMs.

North American Datum of 1927: The datum used on most large scale USGS topographic maps.

Stands for North American Datum 1927. The precursor to WGS84. Many maps still use the NAD27 datum, so always check before using a GPS unit with a map.

The datum used in the early part of the national mapping of the United States. The Clarke 1866 ellipsoid was used and locations and elevations were referenced to a single point at Meade’s Ranch in Kansas.