Introduction to contours by Mr Mohd Salman Ahmed

1. Recap
In the previous classes you have learnt about
• Levelling concepts
• Instruments used
• Errors in levelling
• Classification of levelling
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2. Objectives
On completion of this presentation, you will be able
to know
• Topographic maps
• What is contour ?
• Examples for contours
• Contour interval
• Horizontal equivalent
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3. Topographic map
• Topographic maps have horizontal control
and vertical control
• Points are represented horizontally and
vertically
• Topographic maps give correct picture of
surface of ground
• Topographic map give altitude of points
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4. Topographic map Fig 1
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5. Topographic map Fig 2
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6. Contour
• On level surface all points are of same elevation
• Contour is intersection of level surface and ground
surface
• Contour is an imaginary line passing through points of
same elevation
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7. Contour
• The process of locating contours is called contouring
• Contour line represent altitude on maps
Fig. 3 Contouring
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8. Examples of Contour
• Shore line of water surface of still pond
Fig. 4 Pond view
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9. Examples of Contours
Shore line of water surface in a depression
Fig. 5 Depression
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10. Contour Interval
• The difference of elevation between two consecutive
contours
• Contour interval=5
Fig. 6 Contour interval
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11. Contour Interval (contd.)
• It depends on nature of the ground
• It depends on time & expense of field and office work
• When contour interval is small the time and
expenditure is more
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12. Contour Interval (contd.)
• It depends on purpose &extent of survey
• Contour interval may be small when detailed
information is required
• It will be large when area of survey is vast
• It depends on scale of the map
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13. Contour Interval (contd.)
• For building sites 0.25 to 0.50 m
• For reservoirs, town planning schemes 0.5 to 2m
• Location surveys 2 to 3m
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14. Horizontal Equivalent
 The horizontal distance between any two
consecutive contours
 It depends on nature of ground
 It depends on steepness of country
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15. Summary
We have discussed
 Topographic maps
 Level surface
 Contour line
 Contouring
 Contour interval
 Horizontal equivalent
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16. Quiz
1. A line passing through the points of same elevation is
called
A.Vertical line
B.Horizontal line
C.Contour line
D.Perimeter
Ans: C
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17. 2. A surface on which all points are of equal
elevation is called
A.Level surface
B.Concave surface
C.Convex surface
D.Horizontal surface
Ans: A
Quiz (contd.)
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18. 3. The following is example for level surface
A.Water surface in a river
B.Water surface in a stream
C.Water surface in a still lake
D.Water surface in a reservoir
Ans: C
Quiz (contd.)
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19. Frequently asked questions
1. What is a topographic map?
2. Define level surface and contour ?
3. Differentiate between contour interval and horizontal
equivalent ?
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20. Than Q
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