##### Types of Levelling in surveying

Levelling is an art of determining relative altitudes of points on the surface of the earth or beneath the surface of the earth. It is used to find the elevation of given points with respect to a given or assumed datum and to establish points at a given elevation or at different elevations with respect to a given or assumed datum. Levelling deals with measurements in a vertical plane. Finding out elevation is necessary to enable the work and establishing point, that are necessary in the setting out of works.

**Simple Levelling:**

The operation of levelling for determining the difference in elevation, if not too great, between two points visible from a single position of the level, is known as simple levelling.

**Differential Levelling:**

The method of levelling for determining the difference in elevation of two points either too far or obstructed by an intervening ground, is known as differential levelling. The level is set up at number of points and the difference in elevation of successive points, is determined in this method.

**Check Levelling**

After the completion of fly levelling, level lines are run to check the accuracy of the bench marks previously fixed which is called check levelling.

**Profile Levelling:**

The operation of levelling carried out to determine the elevations of the points at known distances apart, and also salient features, along a given straight line is called profile levelling. It is also known as longitudinal levelling.

**Cross-section levelling**

The operation of levelling which is carried out to provide levels on either side of the main line at right angles, in order to determine the vertical section of the earth surface on the ground is called cross section levelling.

**Reciprocal levelling:**

When the level is not possible to be set up between two points due to an intervening obstruction as large water bodies, reciprocal levelling is carried out. The two sets of reciprocal levelling are done to find out the difference in elevation between two points accurately.