Theory
The method in which spot level taken on already fixed point over the entire area. This respective reduce level (RL) uniform against each point on plan drawn to scale and contour line drawn by intersection is called indirect method contouring by indirect method is done by method of square.
Instrument required
1. Dumpy level
2. Levelling staff
3. Ranging rod
4. Chain
5. Tape
6. Tripod
Diagram
Procedure
This method is suitable of area is not very extensive. In this method the area (200 m x 200 m) is divided into series of squares and the corners of the squares are marked with pegs. The size of the square varies from 5 m to 20 m side depending upon the nature of the same size through out. Each separate square is pegged out. The elevation of the ground at the corners of the squares are determined with a level.
Intermediate points within the squares may be taken when required and may be located on the diagonals of the square or by the measurement from the corners. The system of squares is plotted and near each corner is written its elevation. The contour lines are then interploted in the usual way.
Uses
1. It is used for military and engineering purpose.
2. It can divide grade of pipe lines cannel.
3. Contour may be used to determine the area of chainage basin and capacity of surveiour.
4. Inter visibally of two given points can be ascertained from the map.
5. Quantities of earth work may be compacted from the contour map.
