The general principles of surveying are:
1. To work from the whole to the part
2. To locate a new station by at least two measurements (linear or angular) from fixed reference points.
According to the first principle, the whole area is first enclosed by main stations (i.e. Controlling stations) and main survey lines (i.e. controlling lines). The area is then divided into a number of parts by forming well conditioned triangles. A nearly equilateral triangle is considered to be the best well-conditioned triangle.The main survey lines are measured very accurately with a standard chain. Then the sides of the triangles are measured. The purpose of this process of working is to prevent accumulation of error. During the procedure, if there is any error in the measurement of any side of a triangle, then it will not affect the whole work. The error can always be detected and eliminated.
According to the second principle, the new stations should always be fixed by at least two measurements (linear or angular) from fixed reference points. Linear measurements refer to horizontal distances measured by chain or tape. Angular measurements refer to the magnetic bearing or horizontal angle taken by a prismatic compass or theodolite.
In chain surveying, the positions of main stations and directions of main survey lines are fixed by tie lines and check lines.
