1. Unit 6: Contouring Topics covered Basic definitions
Characterstics of coutour
Unit 10: Contouring

2. Plan or map Only shows the horizontal position of points
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3. Topographic map
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4. Different methods of showing elevations
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5. 10.1 Basic definitions- Contour
The most common method of representing the topography of an area is to use contour lines
Contours
A contour line is an imaginary line that connects points of equal elevation
If you walk along a contour line you neither gain or lose elevation.  
they allow us to show the shape of the land surface (topography) on a map
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6. 10.1 Basic definitions Source: www.raider.muc.edu
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7. 10.1 Basic definitions Source: www.raider.muc.edu
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8. 10.1 Basic definitions Source: www.raider.muc.edu
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9. 10.1 Basic definitions
Imagine a hill that has its top sliced off with a really big knife
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10. 10.2 Contour interval Contour interval
Contour lines can be drawn for any elevation, but to simplify things only lines for certain elevations are drawn on a topographic map
These elevations are chosen to be evenly spaced vertically
This vertical spacing is referred to as the contour interval
The vertical distance between two consecutive contours is Kept constant for a contour plan
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11. 10.2 Contour interval Choice of Contour interval depends upon:
The nature of ground
For flat ground, small interval is chosen
For undulated, broken ground greater (relative term) interval is chosen
The scale of the map
Inversely proportional to the scale of map
For general topographical work, following rules can be followed
The purpose and extent of survey
For detailed design work or accurate earthwork calculation, small interval is chosen
For large extent work such as drainage area, lines of communication, large interval is chosen
Time and expense of field and office work
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12. Horizontal equivalent
The horizontal distance between two points on two consecutive contours
Depends up on the steepness of the ground
Large horizontal equivalent
Small horizontal equivalent
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13. Index contour Index contour
It is not possible to label the elevation of each contour line
To make the map easier to read every fifth contour line is marked with elevation. This contour line is an index contour
Index contours are shown by darker brown lines on the map
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14. 10.2 Characteristics of contour
Closely spaced contours indicate steep slopes
Widely spaced contours indicate moderate slopes
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A contour line must close itself, though not necessarily within the limits of the map
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15. 10.2 Characteristics of contour
Depression and hill look the same; note the contour value to distinguish the terrain
Depression without outlet
Hill
Source: Surveying Vol I by B.C. Punmia
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16. 10.2 Characteristics of contour
Contour lines tend to parallel each other on uniform slopes
Contour lines are parallel, straight and equally spaced in case of inclined plane surface
Source: Surveying Vol I by B.C. Punmia
A contour passing through any point is perpendicular to the line of steepest slope at that point
Source: Surveying Vol I by B.C. Punmia
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17. 10.2 Characteristics of contour
Contour line do not cross except in the case of overhanging cliff or a cave.
Source: Surveying Vol I by B.C. Punmia
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18. 10.2 Characteristics of contour
Contour lines of different elevation can unite to form one line only in the case of a vertical cliff.
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19. 10.2 Characteristics of contour
Contour lines cross a watershed or ridge and valley line at right angle
Watershed or ridge line form curves of U-shape round it with the concave side of the curve towards the higher ground
Valley line form sharp curves of V-shape across it with convex side of the curve towards the higher ground
Source: Surveying Principle and Applications by Barry F. Kavanagh & S.J. Glenn Bird
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20. 10.2 Characteristics of contour
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21. 10.2 Characteristics of contour
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22. Thank you for your attention!
Any questions? Querries?
Unit 10: Contouring