To locate contour gradient, level is set at a commanding position and reading on staff at first point is taken.

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.

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.

In indirect method, each contour is located by determining positions of series of points through which contour passes. The operation is also sometimes called tracing out contours.

Two contour lines of different elevations cannot cross each or. However, contour lines of different elevations can intersect only in case of an overhanging Cliff and a cave.

The Contour maps are useful to determine intersection of surfaces and measurements of earthwork. 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.

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.

Contour lines cross a watershed or ridge line at right angles. The form curves of U shape round it with concave side of curve towards higher ground.

If re are irregularities in surface between two cross lines, additional guide points may be located on intermediate cross lines. If required, some of cross lines may also be chosen at any inclination or 90° to main line.

A Contour passing through any point is perpendicular to line of steepest slope at point. This agrees with since perpendicular distance between contour lines is shortest distance.