Disadvantage of chain surveying is that, in it distances are measured only and therefore with a network of triangles area is to be covered. If the length and angle of a line can be measured with respect to a known direction then it is possible to plot a line, independent of length of other lines. Therefore, in such cases there is no pressure of going only for a network of triangles. Compass can be used to measure the direction with respect to magnetic north-south of a survey line. The magnetic north-south direction which is the reference direction is called meridian (reference direction) and the angle between the line and the meridian is known as bearing. Use of compass for measuring direction of line simplifies the surveying to a great extent.
Construction of different types of compasses, some problems associated with measurement with compass, the system of noting bearings of the lines are described and then field work involved in compass survey is presented.