Leveling is the general term applied to any of the various processes by which
elevations of points or differences in elevation are determined. It is a vital operation
in producing necessary data for mapping, engineering design, and construction.
Leveling results are used to (1) design highways, railroads, canals, sewers,
water supply systems, and other facilities having grade lines that best conform
to existing topography; (2) lay out construction projects according to planned
elevations; (3) calculate volumes of earthwork and other materials; (4) investigate
drainage characteristics of an area; (5) develop maps showing general ground configurations;
and (6) study earth subsidence and crustal motion.