# Contours

## Give the terms used in contours for each of the following

#### Question 1

A number preceded by a dot.

Spot height

#### Question 2

The numerical difference between two contour lines.

Vertical interval

#### Question 3

A number preceded by a triangle.

Triangulation point

#### Question 4

The difference between maximum and minimum height in areas of steep slope.

Relative height

#### Question 5

The accurate height of some point marked above the ground.

Spot height

## Describe the following terms

#### Question 1

Contour Interval

Contour interval means the difference of height between two consecutive contours. For example, if one thick contour shows the height 300 metres and the next thin contour depicts the height of 320 metres. Then, the contour interval is 20 metres.

#### Question 2

Vertical Interval

The vertical distance between any two contour lines is called vertical interval.

#### Question 3

Horizontal Equivalent

The actual distance between two points on two contour lines is called horizontal equivalent.

#### Question 4

The ratio between the vertical height and the horizontal distance of a slope of land measured along the ground is called gradient.

## Explain how would you distinguish between the following on the basis of contours

#### Question 1

Gentle Slope and Steep Slope

Gentle SlopeSteep Slope
In gentle slopes, the change of elevation is gradual. Normally about 1:25 gradient of elevation is gradual.Steep slope suddenly slopes up or down.
The contours are placed wide apart in gentle slope.For steep slopes, the contours are drawn close to one another.

#### Question 2

Scarp and Dip

ScarpDip
A scarp has a narrow top with a steep slope.A dip has a narrow top with a gentle slope.
The contour lines are closer to each other.The contour lines are spread far apart.

#### Question 3

Ridge and Water Divide

RidgeWater Divide
It is a long and narrow highland sloping steeply downwards on its sides.A line which separates two adjacent drainage basins is known as water divide.
Contours showing a ridge are elongated and are closely spaced.The side on which the ridge is steeper, the contours are drawn closely together, whereas the side on which the ridge is gentle, the contours are drawn far apart.

#### Question 4

Peak and Depression

PeakDepression
The highest point of a mountain is known as a mountain peak.A depression is formed when there is a sudden decrease in height at the top of a conical hill.
Contours showing a conical mountain are almost circular with peak of the mountain as their centre. The contours are drawn almost at regular distances, the value of which increases towards the centre, which is the peak and represented with a dot.Contours showing a depression are almost circular like a conical hill with a depression as their centre. The contour lines are drawn at regular distances, and their value keeps on increasing towards the centre, where the lines suddenly show decrease in height at the centre, which is the depression.

#### Question 1

What is meant by 'relief'?

Relief refers to actual configuration of land which includes its altitude and slope. The relief features found on the earth's surface include mountains, valleys, hills, plains and plateaus.

#### Question 2

State the three methods used to show the earth's relief features on a map.

The three methods used to show the earth's relief features are-

1. hachures
3. contours

#### Question 3

What is a 'contour'?

Contour lines are imaginary lines which are drawn on a map to join places having the same height above the mean sea level.

#### Question 4

What do the contour lines represent?

Contour lines are imaginary lines joining places which have the same height above mean sea level.

#### Question 5

Hill shading and hachuring only give an impression of the slope but do not indicate the heights of the land above sea level, whereas the contours show both impression of the slope as well as the heights of the land above the sea level.

#### Question 6

How do contour lines show different slopes of land?

The contour lines are shown by brown colour as thick brown lines and thin brown lines. Contour lines show:

1. Elevation of land: The height of a contour is indicated by figures inserted in a break in the line.

2. Steepness of its slope: When the contours are very close, they represent steep slopes. When they are farther apart, they represent gradually increasing slopes. Absence of contour lines indicate that the land is flat i.e., a low land.

3. Shape of land at various heights: The contour lines indicate the shape of land. For example, almost circular contours whose value decreases inside represent a lake.

#### Question 7

What do you understand by V.I. and H.E.?

V.I. stands for vertical interval. It is the vertical distance between any two contour lines.

H.E. stands for horizontal equivalent. It is the actual distance between two points on two contour lines.

#### Question 8

Give two points of difference between Bench Mark and Spot Height.

Bench MarkSpot Height
These are marks etched on stone or a building to indicate the accurate height determined by surveys.It refers to the height of a point on the ground above the mean sea level.
It is written as "BM" followed by a number.It is represented by a dot followed by a number on the map.

#### Question 9

Why do the contour of different heights not cross each other?

Two contours never intersect each other because each line represents a different height, and we can't have two different heights at the same point.

#### Question 10

How do the contour lines show the direction of the flow of rivers and streams?

Rivers and streams are shown on the map with blue colour. Generally water flows from higher altitude to lower altitude. Since the contours indicate the elevation of land, we can use them to find the direction of a river or stream.

The rivers and streams usually flow from contours representing greater elevations to contours representing lower elevations. The course of a well-developed river can be divided into three stages - upper, middle and lower course; each of which can be recognised with the help of contour lines.

## Symbols and Conventional Signs

#### Question 1

Given below are some symbols and conventional signs, name each one:

1. Kiln
2. Tank with Embankment
3. Permanent huts
4. Temple
5. Lighthouse
6. Triangulated station
7. Benchmark
8. Post office
10. Police station
11. Hospital
12. Powerline with pylons surveyed

#### Question 2

Complete the following by drawing the conventional sign/symbol in the blank boxes:

## Project / Activity

#### Question 1

Draw conventional symbols for the following using appropriate colours where necessary.

(i) Cart-track

(ii) Broken ground

(iii) Nala

(iv) Perennial tank

(v) Stream

(vi) Dry-stream