ABSTRACT
Plane surveying has traditionally relied on an imaginary at reference surface, or datum, with Cartesian axes. This rectangular system is used to describe measured positions by ordered pairs, usually expressed in northings and eastings, or y-and xcoordinates. Even though surveyors have always known that this assumption of a at earth is fundamentally unrealistic, it provided, and continues to provide, an adequate arrangement for small areas. The attachment of elevations to such horizontal coordinates somewhat acknowledges the topographic irregularity of the earth, but the whole system is always undone by its inherent inaccuracy as surveys grow large.
