A datum is a mathematical model of the earth
used to calculate the coordinates on a map, chart, or survey system.
This includes a set of defining parameters, which forms the basis
for computing positions on the surface of the earth. These parameters
include the dimensions of a reference
ellipsoid and the coordinates of a point of origin. Most datums
are created for use only in specific areas of the earth, but the
World Geodetic Systems (WGS) can be used globally.

Datums are important because to accurately represent
horizontal positions on maps and charts, we need a mathematical
model of the earth that takes into consideration the size and shape
of the earth. It is important to know which datum is being used
on a map because the coordinates for a point on the earth’s surface
in one datum will not match the coordinates from another datum for
that same point. These different systems can be translated into
each other very rapidly through the use of sophisticated computer
algorithms.

Geodetic datums are a part of geodesy [See Table 1].
Prior to World War II, geodesy
was primarily concerned with the creation of national control surveys
each of which had it's own geodetic datum. This created a lack of
accuracy and made inconsistencies with actual location of a point
on the earth. There were so many different datums in use that a
same position could be found in different locations on a map. Therefore,
new datums were created which covered larger areas and which have
a higher accuracy. (Maling,1989)