The horizontal control in Geodetic survey is established either by triangulation or by precise traverse. In triangulation, the system consists of a number of inter-connected triangles in which the length of only one line, called the base line and the angles of the triangles are measured very precisely. Knowing the length of one side and the three angles, the lengths of the other two sides of each triangle can be computed. The apexes of the triangles are known as the triangulation nations and the whole figure is called the triangulation system or triangulation figure. The defect of triangulation is that it tens to accumulate errors of length and azimuth, since the length and azimuth of each line is based on the length and azimuth of the preceding, for example To control the accumulation of errors, subsidiary bases are also selected with certain stations, astronomical observation for azimuth and longitude are also made.

To provide the most accurate system of horizontal control points on which the less precise triangles may be based, which in turn may form a framework to which topographical, hydro-graphical, engineering and other surveys may be referred. To assist in the determination of the size and shape of the earth by making observations for latitude, longitude and gravity.