1. Determining surface locations. Conventional plane surveying is done using level and chain, stadia, transit, plane table, or other methods. Location networks may be resolved by traversing, triangulation, or trilateration. Surveys over larger areas require corrections for earth curvature; see spherical excess and Legendre theorem. Various radio, sonic, and satellite positioning methods (q.v.) are used in marine and airborne work. Today the global positioning system (q.v.) is the primary way of determining locations. 2. Carrying out other types of measurements as a function of location.