The art of determining relative positions of objects on the surface of the earth by taking measurements in the horizontal and vertical planes , is called surveying.
Surveying may primarily divided into the following types:
a) Plane Surveying:
The surveys in which the curvature of earth is not taken into consideration are known as plane surveys. These surveys extend over small areas.he degree of accuracy obtained in this type of surveying is comparatively low.Generally areas less than 250 sq. kilometers are treated as plane.When the surveys extend over limited areas,the difference in length between the arc and subtended chord for any two points on the surfaceof the earth is only about 0.1 m for a distance of 18.2 km,0.3 m for 4.3 km and 0.5m for 91 km. Similiarly,the difference between the sum of the angles of a spherical triangle on the earth’s surface and that of the angles of the corresponding plane triangle is only one second for every 195.5 sq. km of area.
The surveys in which the curvature of the earth is taken into account is called geodetic surveying.These surveys extend over large areas( more than 250 square km) and where the degree of accuracy required is great.