Most surveys of small areas are based on the assumption that the Earth’s surface
is a plane. However, as explained in Chapter 19, for large-area surveys it is necessary
to consider Earth curvature. Unfortunately, the calculations necessary to
determine geodetic positions from survey observations and get distances and
azimuths from them are lengthy, and practicing surveyors often are not familiar
with these procedures. Clearly, a system for specifying positions of geodetic
stations using plane rectangular coordinates is desirable, since it allows computations
to be made using simple coordinate geometry formulas, such as those presented
in Chapter 11. The National Geodetic Survey (NGS) met this need by
developing a state plane coordinate system for each state.