Interpreting Topographical Maps
ICSE Class 8 · Geography · Chapter 1
What this chapter covers
- Topographical sheets and the problem of height
- Contours: meaning
- Interpreting contours: height and shape
- Slopes: steep and gentle
- Landforms from contours: hills, plateaus, ridges and valleys
- Gap, saddle, col and pass
- Drawing contours and landforms on plain paper
- Settlement patterns on a toposheet
- Interpreting a toposheet
Key points
- A topographical sheet is a large-scale map showing natural and human-made features; in India it is prepared by the Survey of India.
- A contour joins places of the same height above mean sea level and is shown in brown.
- The contour interval is the fixed height difference between neighbouring contours; spot heights give exact heights at points.
- Contours never cross except at a rare overhanging cliff, always close somewhere, and rise in value towards higher ground.
- Close contours show a steep slope; wide-apart contours show a gentle slope.
- Closed loops rising to the centre show a hill; a crowded edge with an empty centre shows a plateau; long oval loops show a ridge.
- V-shaped contours pointing uphill show a valley.
- A saddle is a broad dip on a ridge, a col a narrow one, a gap a cut right through it, and a pass a route across a range.
- Settlements are shown in red and may be temporary or permanent.
- Nucleated settlements cluster, dispersed ones scatter, and linear ones follow a road, river, canal or coast.
- Interpreting a toposheet means reading relief, drainage, land use, settlements and communications together and explaining the links between them.
Questions answered
What is a contour?
A contour is an imaginary line on a map joining all places of the same height above mean sea level.
Neighbouring contours on a sheet read 150, 175 and 200. What is the contour interval?
175 m − 150 m = 25 m.
Why do two contours of different values normally never cross?
Where two lines crossed, one point would have two different heights, which is impossible on ordinary ground; only at a rare overhanging cliff can lines cross.
How can you tell a steep slope from a gentle slope on a toposheet?
Contours lie close together on a steep slope and far apart on a gentle slope.
Describe the contour pattern of a plateau.
Closed contours crowded together around the edge show steep sides, and a wide space with no further lines inside the highest contour shows the flat top.
In a valley, which way does the point of the V-shaped contour face?
Towards higher ground, and a stream usually runs through the points of the Vs.
How is a col different from a saddle?
Both are dips on a ridge between two high points, but a col is narrower and deeper, while a saddle is broad and shallow.
Why is a pass named for its use rather than its shape?
Any low point on a range or ridge, whether a gap, col or saddle, becomes a pass when people use it as a route across.