Topographical Maps, Class 11 Practical Work in Geography

What Topographical Maps is about

Key concepts

Topographical maps and the Survey of India series

NCERT section Topographical Maps (introduction)

Topographical (general purpose) maps: relatively large-scale maps showing natural and cultural features (relief, vegetation, water bodies, cultivated land, settlements, transport). They are of utmost importance to geographers as base maps for drawing all other maps. Prepared by each country's national mapping organisation: in India, the Survey of India.

Series: maps are drawn as series at different scales; within a series all use the same reference point, scale, projection, conventional signs, symbols and colours.

Two series in India:
1. India and Adjacent Countries Series: prepared until the Delhi Survey Conference of 1937; then maps of adjoining countries were abandoned and the Survey of India mapped only India to International Map Series specifications, but kept the numbering system and layout of the old series.
2. International Map Series of the World: standardised maps of the whole world at 1:1,000,000 and 1:250,000.

Scales and coverage (Figure 5.1):

Scale	Coverage
1:1,000,000	4° × 4°
1:250,000	1° × 1°
1:125,000	30' × 30'
1:50,000	15' × 15'
1:25,000	5' × 7'30"

Reading a topographical map: get acquainted with the legend, conventional signs and colours (Figure 5.2).

Worked example

How many 1:50,000 sheets cover the area of one 1:250,000 sheet? (2 marks)

Try it first, then show the solutionSolution

1. A 1:250,000 sheet covers 1° × 1° = 60' × 60'; a 1:50,000 sheet covers 15' × 15'.
2. Number = (60 ÷ 15) × (60 ÷ 15) = 4 × 4 = 16.

Answer: 16 sheets.

Methods of relief representation and contours

NCERT section Methods of Relief Representation; Contours

Relief features: the elevations and depressions of the earth's surface; a map showing them is a relief map.

Methods: hachures (short lines along the direction of maximum slope, across contours), hill shading, layer tints, benchmarks and spot heights, and contours. Contours and spot heights are mainly used on topographical maps.

Contours: imaginary lines joining places of equal elevation above mean sea level ('level lines'); a map of landforms by contours is a contour map. Earlier drawn by ground surveys and levelling; now largely from aerial photographs.

Vertical interval (VI): the height difference between successive contours (e.g. 20, 50, 100 m); constant on a map; in metres.
Horizontal equivalent (HE): the horizontal distance between contours; large for gentle slopes, small for steep slopes.

Basic features of contours:

• They join places of equal height.
• Their shapes show the height and slope of landforms.
• Closely spaced = steep; widely spaced = gentle.
• Contours that merge show vertical slopes such as cliffs or waterfalls.
• Contours of different heights usually do not cross.

Gradient (from VI and HE): gradient = VI ÷ HE (in the same units), often written '1 in n'.

Worked example

On a 1:50,000 sheet with a VI of 100 m, two contours are 0.8 cm apart. Find the horizontal equivalent and the gradient. (2 marks)

Try it first, then show the solutionSolution

1. HE = 0.8 cm × 50,000 = 40,000 cm = 400 m.
2. Gradient = VI ÷ HE = 100 ÷ 400 = 1/4, i.e. 1 in 4 (a steep slope).

Answer: HE 400 m; gradient 1 in 4.

Types of slope from contours

NCERT section Contours

Slope	Description	Contour pattern
Gentle	Low degree or angle of slope	Contours far apart
Steep	High angle of slope	Contours close together
Concave	Gentle in the lower part, steep in the upper part	Wide spacing at the bottom, close at the top
Convex	Gentle in the upper part, steep in the lower part	Wide spacing at the top, close at the bottom
Irregular/undulating	Mixed	Uneven spacing

Tip: read contour values to know which way is up; then compare spacing at the top and bottom of the slope.

Worked example

On a slope, contours from 100 m to 200 m are widely spaced, and from 200 m to 400 m very close together. Name the slope. (1 mark)

Try it first, then show the solutionSolution

1. Wide spacing in the lower part means gentle there; close spacing in the upper part means steep there.
2. Gentle below and steep above is a concave slope.

Answer: Concave slope.

Landforms from contours

NCERT section Contours

Landform	Description	Contour pattern
Conical hill	Rises almost uniformly, narrow top	Concentric contours at almost regular intervals
Plateau	Wide flat-topped highland with steep sides	Contours close at the margins, the innermost with a wide gap between its sides
V-shaped valley	In mountains, like the letter V	Innermost contour has the lowest value and a very small gap; values increase outward
U-shaped valley	Glacial; flat wide floor, steep sides	Innermost (lowest) contour with a wide gap; values increase outward
Gorge	Deep narrow valley, very steep sides; vertical erosion dominant at high altitudes	Very closely spaced contours; innermost with a small gap
Spur	Tongue of high land projecting into lower ground	V-shaped contours reversed: arms point to higher ground, apex to lower ground
Cliff	Very steep, almost perpendicular face	Contours run very close and merge into one
Waterfall and rapids	Sudden vertical descent of water; rapids are cascades up- or downstream	Contours merge while crossing the stream (waterfall); rapids shown by relatively distant contours across the stream

Valley vs spur: in a valley the V points upstream (to higher ground) with the lowest value inside; in a spur the apex points down to lower ground with the highest value inside.

Worked example

A set of V-shaped contours has its apex pointing towards lower contour values and arms opening towards higher values. Is it a valley or a spur? (2 marks)

Try it first, then show the solutionSolution

1. In a spur the arms of the V point to higher ground and the apex to lower ground.
2. Here the apex points to lower values, so the land projects downward: a spur.

Answer: A spur.

Drawing a cross-section

NCERT section Contours

Cross-section (profile): a side view of the ground cut vertically along a straight line.

Steps (NCERT):
1. Draw a straight line AB across the contours on the map.
2. Place the edge of a strip of paper (or graph paper) along AB.
3. Mark the position and value of every contour that cuts AB.
4. Choose a suitable vertical scale (e.g. ½ cm = 100 m); draw parallel horizontal lines equal in length to AB, at least as many as the contours.
5. Number these lines with the contour values, starting from the lowest.
6. Place the marked strip along the bottom line so A and B match, and mark the contour points.
7. Draw perpendiculars from each point up to the line of its value.
8. Join the points smoothly to get the profile.

Worked example

A line AB on a contour map crosses contours of 200, 300, 400, 300 and 200 m. Without drawing, describe the profile you would get. (2 marks)

Try it first, then show the solutionSolution

1. Heights rise from 200 m to 400 m and then fall back to 200 m along AB.
2. Plotting these heights at their positions and joining them gives a hill profile with its top near the 400 m crossing.

Answer: A hill (ridge) profile rising to about 400 m in the middle.

Cultural features: settlements and transport

NCERT section Identification of Cultural Features from Topographical Sheets

Cultural features: settlements, buildings, roads and railways, shown by conventional signs, symbols and colours; their location and pattern help understand the area.

Settlements: studied by site, location, pattern, alignment and density; compare the settlement map with the contour map to understand patterns.

• Rural types: compact, scattered, linear, circular.
• Urban types: cross-road town, nodal point, market centre, hill station, coastal resort centre, port, manufacturing centre with suburban villages or satellite towns, capital town, religious centre.
• Site factors: water source, food supply, relief, occupation, defence.
• Density is directly related to food supply.
• Linear settlements: aligned along a river valley, road, embankment or coastline.
• Cross-road town: fan-shaped, houses along the roads, the crossing at the heart as the main market. Nodal town: roads radiate in all directions.

Transport and communication: relief, population, size and resource development affect the type and density of transport; shown by conventional signs and useful in understanding the area.

Worked example

On a sheet, a row of villages runs along the bank of a river and a road. Name the settlement pattern and give one reason. (2 marks)

Try it first, then show the solutionSolution

1. Villages aligned along a river valley, road, embankment or coast form linear settlements.
2. They follow the river and road for water supply and easy transport.

Answer: Linear settlement, following water and transport lines.

Interpretation of topographical maps

NCERT section Interpretation of Topographical Maps; Map Interpretation Procedure

Requirements: knowledge of map language and a sense of direction: first find the north line and scale and orient yourself; know the legend. Conventional signs are internationally accepted, so maps can be read anywhere.

Heads of interpretation:
1. Marginal information: sheet number, location, grid references, extent in degrees and minutes, scale, districts covered.
2. Relief and drainage: plains, plateaus, hills, mountains, peaks, ridges, spurs, slope direction; hills (slope shapes), plateaus (broad, narrow, flat, undulating, dissected), plains (alluvial, glacial, karst, coastal, marshy), mountains (elevation, peaks, passes); rivers, tributaries, valleys and drainage patterns (dendritic, radial, ring, trellis, internal).
3. Land use: forests (dense or thin; reserved, protected, classified/unclassified), agriculture, orchards, wasteland, industry, services (schools, colleges, hospitals, parks, airports, substations).
4. Transport and communication: national and state highways, district roads, cart tracks, camel tracks, footpaths, railways, waterways, communication lines, post offices.
5. Settlements: rural (compact, semi-compact, dispersed, linear) and urban (capital, administrative, religious, port towns, hill stations); occupations inferred from land use and settlement (agriculture in rural areas, lumbering and primitive agriculture in tribal areas, fishing on coasts, services and business in towns).

Procedure: (i) use the index number to locate the area in India and its physiographic setting; note scale and contour interval; (ii) trace major landforms, drainage, land use, and settlement and transport on separate tracing sheets; (iii) describe each pattern; (iv) superimpose pairs to find relationships (e.g. contours over land use shows slope versus land use). Aerial photographs and satellite images at the same scale can update the map.

Worked example

Why would you superimpose a contour tracing on a land-use tracing during interpretation? (2 marks)

Try it first, then show the solutionSolution

1. Interpretation looks for causal relationships between features.
2. Overlaying contours on land use shows how slope relates to land use, e.g. cultivation on gentle slopes and forest on steep slopes.

Answer: To reveal the relationship between slope and land use.

Topographical Maps in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Landforms from Contours, Drawing Cross-Sections and Interpreting a Topographical Sheet
• Topographical Sheets of the Survey of India, Methods of Showing Relief, Contours and Types of Slope

Topographical Maps: key facts

Sheet scales and coverage

$1:1,000,000=4°\times 4°;1:250,000=1°\times 1°;1:125,000=30^{\prime }\times 30^{\prime };1:50,000=15^{\prime }\times 15^{\prime };1:25,000=5^{\prime }\times 7^{\prime }30"$

16 sheets of 1:50,000 make one 1:250,000 sheet.

Horizontal equivalent

$HE(ground)=mapdistancebetweencontours\times scaledenominator$

Large HE = gentle slope.

Gradient

$Gradient=VI÷HE(sameunits)=1in(HE÷VI)$

VI constant on a sheet.

Spacing rule

$Closecontours=steep;wide=gentle;merged=cliff/waterfall$

Different contours usually do not cross.

Concave vs convex

Concave: wide below, close above | Convex: close below, wide above

Read values to find up-slope.

Valley vs spur

Valley: V apex to higher ground, lowest value inside | Spur: V apex to lower ground

U-valley: wide gap in the innermost contour.

Interpretation heads

1. 1.Marginal information
2. 2.relief and drainage
3. 3.land use
4. 4.transport
5. 5.settlements (and occupation)

Then trace, describe and superimpose.

Settlement types

Rural: compact, scattered, linear, circular; site factors: water, food, relief, occupation, defence

Density follows food supply.

Topographical Maps: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

Tricks to remember Topographical Maps

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Sheet coverage

  '4-1-30-15-5x7.5': 1:1M 4°, 1:250k 1°, 1:125k 30', 1:50k 15', 1:25k 5'×7'30".

  Use it when: Scales and coverage.

• Relief methods

  'Have Some Lovely Big Cakes': Hachures, Shading (hill), Layer tints, Benchmarks/spot heights, Contours.

  Use it when: Methods of relief representation.

• Interpretation heads

  'My Room Looks Totally Settled': Marginal, Relief-drainage, Land use, Transport, Settlement.

  Use it when: Order of interpretation.

• Site factors

  'Water, Food, Relief, Work, War': water, food, relief, occupation, defence.

  Use it when: Settlement site factors.

Where students lose marks in Topographical Maps

The slips examiners see most often, and what to write instead.

• ✗Mistake: Reading a spur as a valley

  Both make V-shaped contours.

  Wrong working

  V-contours with the apex towards lower values marked as a valley.

  Right working

  Apex towards lower values = spur; apex towards higher values (lowest value inside) = valley.

  ✓Do this: Check the contour values before naming.

  Usually costs: Marks in identification.

• ✗Mistake: Swapping concave and convex

  Students guess from the word.

  Wrong working

  Close contours at the top labelled convex.

  Right working

  Concave: gentle below (wide), steep above (close). Convex: gentle above (wide), steep below (close).

  ✓Do this: Concave curves in like a cave: steep at the top.

  Usually costs: Marks in slope questions.

• ✗Mistake: Using the map distance as the HE

  Forgetting to apply the scale.

  Wrong working

  Gradient = 100 m ÷ 0.8 cm.

  Right working

  HE = 0.8 cm × 50,000 = 400 m; gradient = 100 ÷ 400 = 1 in 4.

  ✓Do this: Convert to ground units first.

  Usually costs: Marks in gradient sums.

• ✗Mistake: Wrong sheet coverage

  Mixing up scales.

  Wrong working

  A 1:50,000 sheet covers 30' × 30'.

  Right working

  1:50,000 = 15' × 15'; 1:125,000 = 30' × 30'.

  ✓Do this: Larger scale, smaller coverage.

  Usually costs: Marks in MCQs and viva.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Which two series of topographical maps does the Survey of India use?Show answer

   The India and Adjacent Countries Series (numbering and layout kept) and the International Map Series of the World (1:1,000,000 and 1:250,000).

2. 2.When was the Delhi Survey Conference held?Show answer

   1937.

3. 3.On one sheet, does the vertical interval or the horizontal equivalent stay constant?Show answer

   The vertical interval stays constant; the horizontal equivalent changes with the slope.

4. 4.What is the horizontal equivalent?Show answer

   The horizontal distance between two successive contours; large for gentle slopes.

5. 5.What do merging contours show?Show answer

   Vertical slopes such as cliffs or waterfalls.

6. 6.What are hachures?Show answer

   Short lines drawn along the direction of maximum slope, across contours, showing slope differences.

7. 7.Name the four types of rural settlements identified on maps.Show answer

   Compact, scattered, linear and circular.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Practical exam chapter: 4 marks.
• ☐Topographical maps: general purpose, large scale, base maps; Survey of India; series share scale, projection and symbols.
• ☐Series: India and Adjacent Countries (to 1937) and International Map Series (1:1M, 1:250k).
• ☐Coverage: 4°, 1°, 30', 15', 5'×7'30" for 1:1M, 1:250k, 1:125k, 1:50k, 1:25k.
• ☐Relief: hachures, hill shading, layer tints, benchmarks, spot heights, contours.
• ☐VI constant; HE varies; close = steep, wide = gentle; merge = cliff/waterfall; gradient = VI ÷ HE.
• ☐Concave: steep above; convex: steep below; landforms: conical hill, plateau, V/U valleys, gorge, spur, cliff, waterfall.
• ☐Cross-section: AB line, strip, vertical scale, perpendiculars, smooth curve.
• ☐Settlements: compact, scattered, linear, circular; cross-road (fan) and nodal (radiating) towns.
• ☐Interpretation: marginal info, relief and drainage, land use, transport, settlements; trace, describe, superimpose.

Topographical Maps: frequently asked questions