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Surveying

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
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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
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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.
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Compare Direct and Indirect Contouring Methods

The Comparison of Direct and Indirect Contouring Methods is shown below in tabular form
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How to determine Area of Field using Cross Staff Survey?

Object: – To determine area of field using cross staff survey.

Equipments:
1. Ranging rod – 7 Nos.
2. 30 m Chain – 1 Nos.
3. Arrow – 5 Nos.
4. Metallic tape (30m) – 1 Nos.
5. Cross staff with stand – 1 Nos.

Procedure: –
1. Field work
2. Classroom work

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