Topographic Surveying

Topographic Surveying

Topographic surveying is the process of determining the positions of both natural and man-made features on the earth's surface and the configuration of the terrain.

Contour Lines

A contour line is an imaginary line connecting points of equal elevation. The vertical distance between adjacent contour lines is called the contour interval.

Characteristics of Contours

1. Steep vs. Gentle Slope: Closely spaced contours indicate a steep slope; widely spaced contours indicate a gentle slope.
2. Ridges and Valleys:
   • Ridge: V-shaped contours pointing downhill (towards lower elevations).
   • Valley: V-shaped contours pointing uphill (towards higher elevations).
3. Hills and Depressions:
   • Hill: Closed concentric loops with increasing elevation towards the center.
   • Depression: Closed loops with hachures pointing inward, indicating decreasing elevation.
4. Uniform Slope: Evenly spaced contours.
5. Overhanging Cliff: Contours merge or cross only in the case of an overhanging cliff or a cave.

Interpolation of Contours

Given a grid of spot elevations, contours can be drawn by interpolation.

Methods:

1. Estimation: Visual interpolation.
2. Arithmetic Calculation: Using linear proportion.
3. Graphical Method: Using a scale or triangle.

Plotting Methods

1. Grid Method: Dividing the area into squares and determining elevations at corners.
2. Tracing Paper Method: For complex interpolation.

Solved Problems