Two methods of Contouring are:-
i) DIRECT METHOD
ii) INDIRECT METHOD
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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
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
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.