What is a map datum? Which map datum do I use?
A. A datum is a mathematical model of the Earth which approximates the shape of the Earth, and enables calculations such as position and area to be carried out in a consistent and accurate manner. The datum is physically represented by a framework of ground monuments (i.e., trig stations) whose positions have been accurately measured and calculated on this reference surface. Lines of latitude and longitude on a map or chart are referenced to a specific map datum. Every chart has a map datum reference. The map datum is usually listed in the title block of the chart. If you are comparing GPS coordinates to a chart or map, the map datum in the GPS unit must be set to match the chart or map’s datum for accurate comparison. The datum used to create a chart or map is generally listed in the legend. Click here to view the map datum list for Garmin units.
