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Ramasesh Iyer

What are the Uses of Contours?

Contour maps are very useful since they provide valuable information about the terrain. Some of the uses are as follows:

i) The nature of the ground and its slope can be estimated

ii) Earth work can be estimated for civil engineering projects like road works, railway, canals, dams etc.

What are the methods of Contouring?

Two methods of Contouring are:-

Explain Cross Section Method of Contouring?

Cross section method is most suitable for preparing contour maps for road works, rail works, canals etc.
Typically, this type of land has a very long strip but narrow width.

The steps involved are as follows:
i) The centre line of the strip of land is first marked

ii) Lines perpendicular to the longitudinal strip are marked dividing the strip into equal sections

Explain Squares or Grid Method of Contouring?

Squares or grid method is suitable for contouring of plains or gently sloping grounds.

The steps adopted are as follows:
i) Mark square grids on the land to be surveyed. The grid size would depend on the extent of survey.
Generally a 1m x 1m grid is selected for small works and a larger grid size for large works

Explain Tacheometric Method of Contouring?

Tacheometric method is adopted for contouring of very steep hills.

The steps are as follows:
i) Set up the tacheometer at the top of the steep hill. Tacheometer is a theodolite fitted with stadia diaphragm. The stadia diaphragm has three horizontal parallel hairs instead of one as found in a conventional cross hair diaphragm.

ii) With the help of a tacheometer it is possible to determine the horizontal distance of the point from the telescope as well its vertical level.