The process of establishing or developing intermediate points between two terminal points or end points on a straight line is known as ranging.
Ranging is of two types
The ranging in which intermediate ranging rods are placed in a straight line by direct observation from either end.
Direct ranging is possible only when the end stations are inter visible.
The ranging in which intermediate points are interpolated by reciprocal ranging or running an auxiliary line.
Indirect ranging is done where end points are not visible and the ground is high .