Figure 1-22. Major Datums in Southeast Asia
1-14. The Preferred Datums. After World War II, considerable advancement was achieved in the
reduction of the different national datums and more toward large unified geodetic systems. This was
achieved by readjusting existing surveys and making direct connections between the different systems.
Large geodetic systems such as the North American, European, Russian, and Tokyo systems are
generally limited to the continental boundaries or smaller areas. These large systems are generally
called preferred datums. In military situations, which are limited to single continents, the preferred
datums usually provide the necessary distance and direction information. Thus, for many types of air-
to-surface or intermediate-range missiles, sufficient geodetic coverage is provided by the preferred
1-15. The Four Principal Datums. The four principal datums into which many existing major or local
geodetic systems are presently united are the North American Datum of 1927, the European Datum, the
Tokyo Datum, and the Indian Datum. Numerous minor surveys have been combined into these four
datums to provide geodetic systems for intermediate-range weapons. The general coverage of these
systems is illustrated in Figure 1-23.