SURVEYING, the act or art of deter mining the boundaries, form, area, posi tion, contour, etc., of any portion of the earth's surface, tract of country, coast, etc., by means of measurements taken on the spot; the art of determining the form, area, surface, contour, etc., of any portion of the earth's surface, and de lineating it accurately on a map or plan. Land surveying is the art of applying the principles of geometry and trigonom etry to the measurement of land. The principal operations are laying down or driving base lines and triangles on either side of the base. In large surveys it is desirable to lay down these triangles by measuring each angle with an instru ment called the THEODOLITE (q. v.)., by which the accuracy of the measurement of the sides may be checked. Geodesic surveying comprises all the operations of surveying carried on under the sup position that earth is spheroidal. It em braces marine surveying.
Marine or hydrographical surveying ascertains the forms of coast lines, har bors, etc., and of objects on the shore, the entrances to harbors, channels, their depth, width, etc., the position of shoals,
the depth of water thereon. Mining sur veying may be either for the purpose of determining the situation and position of the shafts, galleries, and other under ground excavations of a mine already in existence; or it may be for determining the proper positions for the shafts, gal leries, etc., of a mine not yet opened. Railway surveying is a comprehensive term, embracing surveys intended to as certain the best line of communication between two given points; it also in cludes all surveys for the construction of aqueducts for the supply of water to towns, etc. Topographical surveying em braces all the operations incident to find ing the contour of a portion of the earth's surface, and the various methods of representing it upon a plane surface. When only a general topographical map of a country is wanted, it is, in general, sufficient to survey the country with ref erence to its fields, roads, rivers, etc.