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## 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.

iii) It is possible to identify suitable site for any project from the contour map of the region.

iv) Inter-visibility of points can be ascertained using contour maps. This is most useful for locating communication towers.

v) Military uses contour maps for strategic planning.

We at engineeringcivil.com are thankful to Mr Ramasesh Iyer for submitting this useful information to us.

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## What are the methods of Contouring?

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

DIRECT METHOD
In direct method, the points of equal elevation on the terrain are physically located and then plotted on map. This is a very tedious process and requires more time and resources than the indirect method.

INDIRECT METHOD
In the indirect method of contouring on of these three methods are adopted:
A) Cross Section Method
B) Squares Or Grid Method
C) Tacheometric Method

We at engineeringcivil.com are thankful to Mr Ramasesh Iyer for submitting this useful information to us.

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## 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

iii) The perpendicular lines are divided into equally spaced divisions, thus forming rectangular grids.

iv) Levels are taken at the intersection of the grid lines to obtain the cross-section profile of the strip of land.

v) Contour map is plotted in the office by interpolating points of equal elevation based on the levels taken at site.

We at engineeringcivil.com are thankful to Mr Ramasesh Iyer for submitting this useful information to us.

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## 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

ii) Levels are taken at all the corners of the square and the intersection of the diagonal.

iii) Levels taken on the intersection of diagonals is used for verification of the interpolation.

vi) Contour map is plotted in the office by interpolating points of equal elevation based on the levels taken on the corners of the square.

We at engineeringcivil.com are thankful to Mr Ramasesh Iyer for submitting this useful information to us.

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## 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.

iii) The steep hill is surveyed at three levels – the base of the hill, the mid-level of the hill and the top level of the hill.

iv) Using the tacheometer reading are taken all around the hill at equal angular intervals on all these three
levels.

v) The radial plot thus obtained is worked in the office to interpolate points of equal elevation for contour mapping.

We at engineeringcivil.com are thankful to Mr Ramasesh Iyer for submitting this useful information to us.

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