Ranging:

In general, the length of the survey line is several times the chain length. Therefore, along the survey lines intermediate points are needs to be located to ensure that the survey lines are located and measured in a straight line. The distance could be directly measured through chain and or tape only if its length is more than that of a survey line. In all another cases, intermediate points help in pulling the chain/tape along the proper survey line on the needed straight line. This procedure of locating intermediate points along a straight line is known as ranging.

If the end survey stations on the survey line are inter-visible, direct ranging through eyes or line rangers is probable. In case of optical obstructions occurring among end stations, reciprocal ranging or indirect ranging is adopted.