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Topographical Maps
Chapter 5
Topographical Maps
You know that the map is an important geographic tool. You also
know that maps are classified on the basis of scale and functions.
The topographical maps, which have been referred to in Chapter 1
are of utmost importance to geographers. They serve the purpose
of base maps and are used to draw all the other maps.
Topographical maps, also known as general purpose maps, are
drawn at relatively large scales. These maps show important natural
and cultural features such as relief, vegetation, water bodies,
cultivated land, settlements, and transportation networks, etc.
These maps are prepared and published by the National Mapping
Organisation of each country. For example, the Survey of India
prepares the topographical maps in India for the entire country.
The topographical maps are drawn in the form of series of maps at
different scales. Hence, in the given series, all maps employ the
same reference point, scale, projection, conventional signs, symbols
and colours.
The topographical maps in India are prepared in two series, i.e.
India and Adjacent Countries Series and The International Map
Series of the World.
India and Adjacent Countries Series: Topographical maps under
India and Adjacent Countries Series were prepared by the Survey
of India till the coming into existence of Delhi Survey Conference
in 1937. Henceforth, the preparation of maps for the adjoining
countries was abandoned and the Survey of India confined itself to
prepare and publish the topographical maps for India as per the
specifications laid down for the International Map Series of the
World. However, the Survey of India for the topographical maps
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Practical Work in Geography
under the new series retained the numbering system and the layout plan
of the abandoned India and Adjacent Countries Series.
The topographical maps of India are prepared on 1 : 10,00,000,
1 : 250,000, 1 : 1,25,000, 1 : 50,000 and 1: 25,000 scale providing a
latitudinal and longitudinal coverage of 4° x 4°, 1° x 1°, 30' x 30', 15' x
15' and 5' x 7' 30", respectively. The numbering system of each one of
these topographical maps is shown in Fig. 5.1 (on page 51).
International Map Series of the World: Topographical Maps
under International Map Series of the World are designed to produce
standardised maps for the entire World on a scale of 1: 10,00,000 and
1:250,000.
Reading of Topographical Maps: The study of topographical maps
is simple. It requires the reader to get acquainted with the legend, conventional
sign and the colours shown on the sheets. The conventional sign and symbols
depicted on the topographical sheets are shown in Fig. 5.2 (on page 52).
Glossary
Contours: Imaginary lines joining all the points of equal elevation or
altitude above mean sea level. They are also called “level lines”.
Contour Interval: Interval between two successive contours. It is also
known as vertical interval, usually written as V. I. Generally, it is constant
for a given map.
Cross-section: A side view of the ground cut vertically along a straight
line. It is also known as a section or profile.
Hachures: Small straight lines drawn on the map along the direction of
maximum slope, running across the contours. They given an idea about
the differences in the slope of the ground.
Topographic Map: A map of a small area drawn on a large scale
depicting detailed surface features both natural and man made. Relief
in this map is shown by contours.
METHODS OF RELIEF REPRESENTATION
The earth’s surface is not uniform and it varies from mountains to hills to
plateaus and plains. The elevation and depressions of the earth’s surface
are known as physical features or relief features of the earth. The map
showing these features is called a relief map.
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Topographical Maps
Figure 5.1 Reference Map of Topographical Sheets Published by Survey of India
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52
Figure 5.2 Conventional Signs and Symbols
A number of methods have been used to show the relief features of
the Earth’s surface on maps, over the years. These methods include
hachure, hill shading, layer tints, benchmarks and spot heights and
contours. However, contours and spot heights are predominantly used
to depict the relief of an area on all topographical maps.
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Topographical Maps
CONTOURS
Contours are imaginary lines joining places having the same elevation
above mean sea level. A map showing the landform of an area by contours
is called a contour map. The method of showing relief features through
contour is very useful and versatile. The contour lines on a map provide
a useful insight into the topography of an area.
Earlier, ground surveys and levelling methods were used to draw
contours on topographical maps. However, the invention of photography
and subsequent use of aerial photography have replaced the conventional
methods of surveying, levelling and mapping. Henceforth, these
photographs are used in topographical mapping.
Contours are drawn at different vertical intervals (VI), like 20, 50, 100
metres above the mean sea level. It is known as contour interval. It is
usually constant on a given map. It is generally expressed in metres.
While the vertical interval between the two successive contour lines remains
constant, the horizontal distance varies from place to place depending
upon the nature of slope. The horizontal distance, also known as the
horizontal equivalent (HE), is large when the slope is gentler and decreases
with increasing slope gradient.
Some basic features of contour lines are
° A contour line is drawn to show places of equal heights.
° Contour lines and their shapes represent the height and slope or
gradient of the landform.
° Closely spaced contours represent steep slopes while widely spaced
contours represent gentle slope.
° When two or more contour lines merge with each other, they represent
features of vertical slopes such as cliffs or waterfalls.
° Two contours of different elevation usually do not cross each other.
Drawing of Contours and Their Cross Sections
We know that all the topographical features show varying degrees of
slopes. For example, a flat plain exhibits gentler slopes and the cliffs and
gorges are associated with the steep slopes. Similarly, valleys and
mountain ranges are also characterised by the varying degree of slopes,
i.e. steep to gentle. Hence, the spacing of contours is significant since it
indicates the slope.
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Gentle Slope Steep Slope
Types of slope
The slopes can broadly be classified into gentle, steep, concave, convex
and irregular or undulating. The contours of different types of slopes
show a distinct spacing pattern.
Gentle Slope
When the degree or angle of
slope of a feature is very low, the
slope will be gentle. The
contours representing this type
of slope are far apart.
Steep Slope
When the degree or angle of
slope of a feature is high and
the contours are closely spaced,
they indicate steep slope.
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Topographical Maps
Concave Slope
A slope with a gentle gradient in
the lower parts of a relief feature
and steep in its upper parts is
called the concave slope.
Contours in this type of slope are
widely spaced in the lower parts
and are closely spaced in the
upper parts.
Convex Slope
Unlike concave slope, the
convex slope is fairly gentle in
the upper part and steep in the
lower part. As a result, the
contours are widely spaced in
the upper parts and are closely
spaced in the lower parts.
Concave Slope Convex Slope
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Types of Landform
Conical Hill
It rises almost uniformly from
the surrounding land. A conical
hill with uniform slope and
narrow top is represented by
concentric contours spaced
almost at regular intervals.
Plateau
A widely stretched flat–topped high
land, with relatively steeper slopes,
rising above the adjoining plain or
sea is called a plateau. The contour
lines representing a plateau are
normally close spaced at the margins
with the innermost contour showing
wide gap between its two sides.
Conical Slope Plateau
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Topographical Maps
VALLEY
A geomorphic feature lying between two hills or ridges and formed as a
result of the lateral erosion by a river or a glacier is called a valley.
‘V’-shaped Valley
It resembles the letter V. A V-shaped
valley occurs in mountainous areas.
The lowermost part of the V–shaped
valley is shown by the innermost
contour line with very small gap
between its two sides and the lowest
value of the contour is assigned to it.
The contour value increases with
uniform intervals for all other contour
lines outward.
‘U’ – shaped Valley
A U–shaped valley is formed by strong
lateral erosion of glaciers at high
altitudes. The flat wide bottom and
steep sides makes it resemble the
letter ‘U’. The lowermost part of the
U–shaped valley is shown by the
innermost contour line with a wide
gap between its two sides. The contour
value increases with uniform intervals
for all other contour lines outward.
V-Shaped Valley U-Shaped Valley
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Gorge
In high altitudes, gorges form in the
areas where the vertical erosion by
river is more prominent than the
lateral erosion. They are deep and
narrow river valleys with very steep
sides. A gorge is represented by very
closely-spaced contour lines on a map
with the innermost contour showing
small gap between its two sides.
Spur
A tongue of land, projecting from
higher ground into the lower is called
a spur. It is also represented by V-
shaped contours but in the reverse
manner. The arms of the V point to
the higher ground and the apex of ‘V’
to the lower ones.
Gorge Spur
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Topographical Maps
CLIFF
It is a very steep or almost
perpendicular face of landform. On a
map, a cliff may be identified by the
way the contours run very close to one
another, ultimately merging into one.
Waterfall and Rapids
A sudden and more or less
perpendicular descent of water from
a considerable height in the bed of a
river is called a waterfall. Sometimes,
a waterfall succeeds or precedes with
a cascading stream forming rapids
upstream or downstream of a
waterfall. The contours representing
a waterfall merge into one another
while crossing a river stream and the
rapids are shown by relatively distant
contour lines on a map.
Cliff Waterfall
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Steps for Drawing a Cross-section
The following steps may be followed to draw cross-sections of various
relief features from their contours :
1. Draw a straight line cutting across the contours on the map and
mark it as AB.
2. Take a strip of white paper or graph and place its edge along the
AB line.
3. Mark the position and value of every contour that cuts the line
AB.
4. Choose a suitable vertical scale, eg ½ cm =100 metres, to draw
horizontal lines parallel to each other and equal to the length of
AB. The number of such lines should be equal or more than the
total contour lines.
5. Mark the appropriate values corresponding to the contour values
along the vertical of the cross-section. The numbering may be
started with the lowest value represented by the contours.
6. Now place the edge of the marked paper along the horizontal line
at the bottom line of the cross-section in such a way that AB of the
paper corresponds to the AB of the map and mark the contour
points.
7. Draw perpendiculars from AB line, intersecting contour lines, to
the corresponding line at the cross-section base.
8. Smoothly join all the points marked on different lines at the cross-
section base.
IDENTIFICATION OF CULTURAL FEATURES FROM
TOPOGRAPHICAL SHEETS
Settlements, buildings, roads and railways are important cultural features
shown on topographical sheets through conventional signs, symbols and
colours. The location and pattern of distribution of different features
help in understanding the area shown on the map.
Distribution Of Settlements
It can be seen in the map through its site, location pattern, alignment and
density. The nature and causes of various settlement patterns may be
clearly understood by comparing the settlement map with the contour
map.
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Topographical Maps
Four types of rural settlements may be identified on the map
(a) Compact
(b) Scattered
(c) Linear
(d) Circular
Similarly, urban centres may also be distinguished as
(a) Cross-road town
(b) Nodal point
(c) Market centre
(d) Hill station
(e) Coastal resort centre
(f) Port
(g) Manufacturing centre with suburban villages or satellite towns
(h) Capital town
(i) Religious centre
Various factors determine thesite of settlements like
(a) Source of water
(b) Provision of food
(c) Nature of relief
(d) Nature and character of occupation
(e) Defence
Site of settlements should be closely examined with reference to the
contour and drainage map. Density of settlement is directly related to
food supply. Sometimes, village settlements form alignments, i.e. they
are spread along a river valley, road, embankment, coastline – these are
called linear settlements.
In the case of an urban settlement, a cross-road town assumes a
fan-shaped pattern, the houses being arranged along the roadside and
the crossing being at the heart of the town and the main market place. In
a nodal town, the roads radiate in all directions.
Transport And Communication Pattern
Relief, population, size and resource development pattern of an area
directly influence the means of transport and communication and their
density. These are depicted through conventional signs and symbols.
Means of transport and communication provide useful information about
the area shown on the map.
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INTERPRETATION OF TOPOGRAPHICAL MAPS
Knowledge of map language and sense of direction are essential in reading
and interpreting topo-sheets .You must first look for the northline and the
scale of the map and orient yourself accordingly. You must have a thorough
knowledge of the legends / key given in the map depicting various features.
All topo-sheets contain a table showing conventional signs and symbols
used in the map (Figure 5.2). Conventional signs and symbols are
internationally accepted; so, anyone can read any map anywhere in the
world without knowing the language of that particular country.
A topographic sheet is usually interpreted under the following heads:
(a) Marginal Information
(b) Relief and Drainage
(c) Land Use
(d) Means of Transport and Communication
(e) Human Settlement
Marginal Information: It includes the topographical sheet number,
its location, grid references, its extent in degrees and minutes, scale, the
districts covered, etc.
Relief of the Area: The general topography of the area is studied to
identify the plains, plateaus, hills or mountains along with peaks, ridges,
spur and the general direction of the slope. These features are studied under
the following heads :
° Hill : With concave, convex, steep or gentle slope and shape.
° Plateau : Whether it is broad , narrow, flat, undulating or dissected.
° Plain: Its types, i.e. alluvial, glacial, karst, coastal, marshy, etc.
° Mountain : General elevation, peak, passes, etc.
Drainage of the Area: The important rivers and their tributaries and
the type and extent of valleys formed by them, the types of drainage pattern,
i.e. dendritic, radial, ring, trellis, internal, etc.
Land Use: It includes the use of land under different categories like :
° Natural vegetation and forest (which part of the area is forested,
whether it is dense forest or thin, and the categories of forest found
there like Reserved, Protected, Classified / Unclassified).
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Topographical Maps
° Agricultural, orchard, wasteland, industrial, etc.
° Facilities and Services such as schools, colleges, hospitals, parks,
airports, electric substations, etc.
Transport and Communication: The means of transportation
include national or state highways, district roads, cart tracks, camel
tracks, footpaths, railways, waterways, major communication lines, post
offices, etc.
Settlement: Settlements are studied under the following heads :
° Rural Settlements: The types and patterns of rural settlements,
i.e. compact, semi-compact, dispersed, linear, etc.
° Urban Settlements: Type of urban settlements and their functions,
i.e. capital cities, administrative towns, religious towns, port towns,
hill stations, etc.
Occupation: The general occupation of the people of the area may be
identified with the help of land use and the type of settlement. For example,
in rural areas the main occupation of majority of the people is agriculture;
in tribal regions, lumbering and primitive agriculture dominates and in
coastal areas, fishing is practised. Similarly, in cities and towns, services
and business appear to be the major occupations of the people.
MAP INTERPRETATION PROCEDURE
Map interpretation involves the study of factors that explain the causal
relationship among several features shown on the map. For example, the
distribution of natural vegetation and cultivated land can be better
understood against the background of landform and drainage. Likewise,
the distribution of settlements can be examined in association with the
levels of transport network system and the nature of topography.
The following steps will help in map interpretation:
° Find out from the index number of the topographical sheet, the
location of the area in India. This would give an idea of the general
characteristics of the major and minor physiographic divisions of
the area. Note the scale of the map and the contour interval, which
will give the extent and general landform of the area.
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° Trace out the following features on tracing sheets.
(a) Major landforms – as shown by contours and other graphical
features.
(b) Drainage and water features – the main river and its important
tributaries.
(c) Land use – i.e. forest, agricultural land, wastes, sanctuary,
park, school, etc.
(d) Settlement and Transport pattern.
° Describe the distributional pattern of each of the features separately
drawing attention to the most important aspect.
° Superimpose pairs of these maps and note down the relationship,
if any, between the two patterns. For example, if a contour map is
superimposed over a land use map, it provides the relationship
between the degree of slope and the type of the land used.
Aerial photographs and satellite imageries of the same area and of the
same scale can also be compared with the topographical map to update
the information.
EXERCISE
1. Answer the following questions in about 30 words:
(i) What are topographical maps?
(ii) Name the organisation which prepares the topographical maps of
India.
(iii) Which are the commonly used scales for mapping our country
used by the Survey of India?
(iv) What are contours?
(v) What does the spacing of contours indicate?
(vi) What are conventional signs?
2. Write short notes on—
(i) Contours
(ii) ‘Marginal Information’ in Topographical sheets
(iii) The Survey of India
3. Explain what is meant by ‘map interpretation’ and what procedure is
followed for its interpretation.
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Topographical Maps
4. If you are interpreting the cultural features from a topographical sheet,
what information would you like to seek and how would you derive
this information? Discuss with the help of suitable examples.
5. Draw the conventional signs and symbols for the following features—
(i) International Boundary
(ii) Bench Mark
(iii) Villages
(iv) Metalled Road
(v) Footpath with bridges
(vi) Places of Worship
(vii)Railwayline
Exercise A
Study the contour pattern and answer the following questions.
1. Name the geographical feature formed by contours.
2. Find out the contour interval in the map.
3. Find out the map distance between E and F and convert it into ground
distance.
4. Name the type of slope between A and B; C and D and E and F.
5. Find out the direction of E, D and F from G.
Exercise B
Study the extract from the topographical sheet No. 63K/12, as shown in
the figure below and answer the following questions—
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1. Convert 1:50,000 into a statement of scale.
2. Name the major settlements of the area.
3. What is the direction of flow of the river Ganga?
45’
82o
40’
25o
82o
45’
25o
82o
40’
25o
82o
10’ 10’
15’
15’
25o
Uttar Pradesh
Mirzapur and Varanasi District Part of 63K/12
R. F. 1: 50,000
Part of the Topographical Sheet No 63K/12
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Topographical Maps
4. At which one of the banks of river Ganga, Bhatauli is located ?
5. What is the pattern of rural settlements along the right bank of river
Ganga?
6. Name the villages/settlements where Post Office is located ?
7. What does the yellow colour in the area refer to?
8. What means of transportation is used to cross the river by the people
of Bhatauli village ?
Exercise C
Study the extract for topographical sheet 63K/12 shown in the figure on
page 68 and answer the following questions.
1. Give the height of the highest point on the map.
2. River Jamtihwa Nadi is flowing through which quarter of the map ?
3. Which is the major settlement located in the east of the Kuardari Nala ?
4. What type of settlement does the area have ?
5. Name the geographical feature represented by white patches in the
middle of Sipu Nadi.
6. Name the two types of vegetation shown on part of the topographical
sheet.
7. What is the direction of the flow of the Kuardari ?
8. In which part of the sheet area is Lower Khajuri Dam located?
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0’
25o
40’
82o
35’
25o
82o
40’
25o
82o
35’
25o
82o
0’
5’
5’
Uttar Pradesh
Mirzapur and Varanasi District Part of 63K/12
R. F. 1: 50,000
Part of the Topographical Sheet No 63K/12
2015-16(20/01/2015)

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