What is a Map Datum ?
A map datum is a mathematical description of the earth or a part of the earth. It is used to correctly assign real-world coordinates to points on a map or a chart. Because the earth has a very irregular shape, taking accurate measurements of doing calculations on the earth’s true surface is very difficult and complicated. A mathematically regular shape is much easier to deal with, if the shape accurately represents the earth’s true shape. The most representative shape is an ellipsoid. A map datum is a mathematical description of the earth or a part of the earth, and is based on the ellipsoid or the arc of an ellipsoid that most closely represents the area being described. In addition, the datum is centered at a specific location know as the datum origin. A datum may describe a small part of the earth, such as WGS84, depending on which ellipsoid or ellipsoidal arc is selected and where the datum origin is. Since datums use different ellipsoids and have different origins, the Latitude an
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 the GPS coordinates to a chart or other reference, the map datum in the GPS unit should be selected to the same map datum that is listed as the datum used to generate the chart or other reference. • What is the MOB function? The Man Over Board (MOB) function is a common feature for marine GPS units. If a person falls overboard, the skipper uses this function to immediately mark the current location. The GPS
