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“ I know that thou canst do every thing, and that no thought can be withholden from thee. “ (Job 42:2)

Contour Survey

Contour line

• The line of intersection of a level surface with the ground surface is known as the contour line or simply the contour. It can also be defined as a line passing through points of equal reduced levels.
• For example, a contour of 100 m indicates that all the points on this line have an RL of 100 m. Similarly, in a contour of 99 m, all points have an RL of 99 m, a map showing only the contour lines of an area is called a contour map.

Contour Interval

• The vertical distance between any two consecutive contours is known as a contour interval. Suppose a map includes contour lines of 100 m, 98 m, 96m, and so on. The contour interval here is 2 m. This interval depends upon: (i) the nature of the ground (i.e. whether flat of steep) (ii) the scale of the map and (iii) the purpose of the survey.
• Contour intervals for flat country are generally small, e.g.0.25 m, 0.50 m, 0.75 m, etc. The contour interval for a steep slope in a hilly area is generally greater, e.g. 5 m, 10 m, 15 m, etc.
• Again, for a small-scale map, the interval may be of 1 m, 2 m, 3 m, etc, and for large scale map, it may be of 0.25 m, 0.50 m, 0.75 m, etc.
• It should be remembered that the contour interval for a particular map is constant.

Horizontal Equivalent

• The horizontal distance between any two consecutive contours is known as horizontal equivalent. It is not constant. It varies according to the steepness of the ground.
• For steep slopes, the contour lines run close together, and for flatter slopes they are widely.

Object Of Preparing Contour Map

• The general map of a country includes the locations of roads, railways, rivers, villages, towns, and so on. But the nature of the ground surface cannot be realized, from such a map.
• However, for all engineering projects involving roads, railways, and so on, a knowledge of the nature of ground surface is required for locating suitable alignments and estimating the volume of earth work.
• Therefore, the contour map is essential for all engineering projects. This why contour maps are prepared.
• A contour may be defined as a line of intersection of a level surface with the surface of the ground. This means every point on the contour line has the same altitude as that of the assumed intersecting surface.
• The process of tracing contour lines on the surface of earth is called contouring. A contour map gives the idea of the altitudes of the surface features as well as their relative positions in a plan.

Uses of Contour Maps

The following are the specific uses of the contour map:
• The nature of the ground surface of a country can be understood by studying a contour map. Hence, the possible route of communication between different places can be demarcated.
• A suitable, site or an economical alignment can be selected for any engineering project.
• The capacity of a reservoir or the area of a catchment can be approximately computed.
• The indivisibility or otherwise of different points can be established.
• A suitable route for a given gradient can be marked on the map.
• A section of the ground surface can be drawn in any direction from the contour map.
• Quantities of earth work can be approximately computed.

Basic Survey

• Cadastral Survey
• GPS, RTK, DGPS Survey
• Final Location Survey
• Contour Survey
• Drawing Digitization
• Construction Survey

• Pipeline Survey
• Topographical Survey
• Land Survey
• Other Services
• Road Survey
• Railway Survey

• Airport Road Survey
• Dam Survey
• Bridge Survey
• Hill Survey
• River Survey
• Engineering Survey

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