Figure 1-23. Preferred Datums
a. The North American Datum of 1927 is used in the United States. It has its origin at Meade's
Ranch, Kansas and is based on Clarke's ellipsoid of 1866.
b. The European Datum's initial point is located in Potsdam, Germany. Numerous national systems
have been joined into a large datum based upon the international ellipsoid. The National Imagery and
Mapping Agency (NIMA) has connected the European and African triangulation chains and filled the
gap of the African arc measurement from Cairo to Cape Town. Thus, all of Europe, the Republic of
South Africa, and north Africa are molded into one system. Through common survey stations, it was
also possible to convert data from the 1932 Russian Pulkova (Pulkovo) system to the European Datum.
As a result, it includes triangulation as far east as the 84th meridian. Additional ties across the Middle
East have permitted connection of the Indian and European Datums.
c. The Tokyo Datum's origin in Tokyo is defined in terms of Bessel's ellipsoid. By means of
triangulation ties through Korea, the Japanese Datum is connected with the Manchurian Datum. The
Tokyo Datum is oriented by means of a single astro-geodetic station. Unfortunately, Tokyo is situated
on a steep geoid slope, and the single station orientation results in large systematic geoid separations as
the system extends from its initial point.
d. The India Datum is accepted as the preferred datum for India and several adjacent countries in
southeast Asia. It is computed on the Everest ellipsoid, with its origin at Kalianpur in central India. The
Everest ellipsoid, derived in 1830, is the oldest of the ellipsoids in common use, although it is much too
small. As a result of the small ellipsoid, the datum cannot be extended too far from the origin or very