The document discusses topographic maps and contour lines. It defines a topographic map as a map that shows both horizontal and vertical control to accurately depict ground surfaces and elevation. Contours are imaginary lines on the map that connect points of equal elevation. The spacing between contours is called the contour interval and depends on factors like terrain, map scale, and purpose. Drawing contours is known as contouring. Examples of contours include shorelines and contour lines on a topographic map help indicate changes in elevation.

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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