Interpolation of contours is process of spacing contours proportionately between plotted ground points established by indirect methods.

Contour gradient is a line lying throughout on surface of ground and preserving a constant inclination to horizontal. If inclination of such a line is given, its direction from a point may be easily located eir on map or on ground.

Two contour lines of different elevations cannot cross each or. If y did, point of intersection would have two different elevations which are absurd.

In indirect method, some suitable guide points are selected and surveyed. The guide points need not necessarily be on contours.

A Contour is an imaginary line on ground joining points of equal elevation. It is a line in which surface of ground is interested in a level surface. A Contour line is a line on map representing a contour.

The line that marks limits of drainage area has following characteristics it passes through every ridge or saddle that divides drainage area from or areas. It often follows ridges.

Estimation method is extremely rough and is used for small scale work only. The positions of contour points between guide points are located by estimation.

If scale is small, contour interval should be large. If scale is large, contour interval should be small.

The contour plan may be used to calculate capacity of a reservoir. Contour maps are also useful to determine Determination of intervisibility between two points, tracing of contour gradient and location of route, calculation of reservoir capacity.

The same contour appears on eir sides of a ridge or valley, for highest horizontal plane that interests ridge must cut it on both sides. The same is true in case of a lower horizontal plane that cuts a valley.