IV.

Geodetic Surveying

For large areas, surveys must take into account the basic shape of the earth, the geoid, and are therefore called geodetic surveys. These surveys are based on a spheroidal shape approximating the geoidal or geographic (nearly spherical) shape of the earth at sea level. They are based on a true north-south meridian as defined by the earth's rotational axis and on spherical geometry. In the U.S., plane-coordinate systems exist for most states, with conversion between plane coordinates and geodetic coordinates made convenient by tabulated relationships. Typically, a highway-route survey extending for many kilometers would require geodetic adjustment to avoid accumulation of error resulting from the convergence of meridians.