WGS-84

The World Geodetic System 1984 is the global geodetic datum on which GPS and the other GNSS constellations compute and report position, defined by an Earth-centered reference ellipsoid and a precise realization of the coordinate frame. Modern ENCs are referenced to WGS-84, so GNSS position overlays directly on the chart. Older paper charts surveyed to a local datum carry a note of the shift to apply, and a charted danger surveyed on a different datum can sit tens or even hundreds of meters from its WGS-84 GNSS position, a recognized grounding hazard.