Class 11 Geography Notes Chapter 5 (Topographical Maps) – Practical Work in Geography Book
Detailed Notes with MCQs of a crucial chapter for your geography practical skills and competitive exams: Chapter 5, Topographical Maps. Understanding these maps is fundamental for analysing the earth's surface in detail.
Chapter 5: Topographical Maps - Detailed Notes for Government Exam Preparation
1. Introduction to Topographical Maps
- Definition: Topographical maps (or 'topo sheets') are large-scale maps that represent, in detail, both natural features (like relief, rivers, forests) and man-made features (like roads, railways, settlements, canals) of a small area.
- Purpose: They provide a comprehensive graphical representation of the terrain, essential for planning, administration, defence, resource management, engineering projects, and geographical analysis.
- Key Characteristic: Their primary distinguishing feature is the detailed representation of relief (elevation and landforms) using contour lines.
- Publishing Authority in India: The Survey of India (SoI) is the principal agency responsible for preparing and publishing topographical maps for the entire country.
2. Scale of Topographical Maps
- Definition: Scale represents the ratio between a distance on the map and the corresponding distance on the ground.
- Large Scale: Topographical maps are large-scale maps, meaning a small area is shown in great detail. The Representative Fraction (RF) is relatively large (e.g., 1:50,000 means 1 unit on the map represents 50,000 units on the ground).
- Common Scales in India (SoI):
- 1:250,000 (Quarter-inch maps - older series, now Degree Sheets)
- 1:50,000 (Most common and detailed for general use)
- 1:25,000 (Very detailed, often for specific projects or densely populated areas)
- Representation of Scale:
- Statement of Scale: Expressed in words (e.g., "2 cm to 1 km" or "1 inch to 1 mile").
- Representative Fraction (RF): A ratio or fraction where the numerator (always 1) represents map distance and the denominator represents ground distance in the same units (e.g., 1:50,000).
- Linear or Graphical Scale: A graduated line printed on the map, allowing direct measurement of distances.
3. Topographical Map Series and Numbering (India & Adjacent Countries Series)
- This is a crucial area for exams.
- Basis: The system is based on the International Map of the World (IMW) specifications.
- Million Sheets (1:1,000,000):
- The world is divided into grids of 4° latitude x 6° longitude.
- India is covered by sheets numbered from 40 upwards (e.g., 45, 53, 54). Each sheet covers 4° x 6°.
- Degree Sheets (1:250,000):
- Each Million Sheet (4°x6°) is divided into 16 Degree Sheets (1° latitude x 1° longitude).
- These are lettered A to P (from NW corner, row by row).
- Example: Sheet 45D covers 1°x1° area within the Million Sheet 45.
- Half-Inch / Inch Sheets (1:126,720 / 1:63,360 - Older Series): Degree sheets were further divided, often used in older surveys.
- Metric Sheets (1:50,000):
- Each Degree Sheet (1°x1° or 60'x60') is divided into 16 sheets.
- These are numbered 1 to 16 (from NW corner, row by row).
- Each sheet covers 15' latitude x 15' longitude.
- Example: Sheet 45 D/10 is one specific 1:50,000 sheet within the Degree Sheet 45D.
- Special Sheets (1:25,000):
- Each 1:50,000 sheet (15'x15') is divided into 4 sheets.
- These are designated by cardinal directions: NW, NE, SW, SE.
- Each sheet covers 7'30" latitude x 7'30" longitude.
- Example: Sheet 45 D/10/NE is a 1:25,000 sheet.
4. Reading and Interpreting Topographical Maps
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A. Marginal Information: Details printed in the map margins are vital.
- Sheet Number: Identifies the specific map (e.g., 45 D/10).
- Location/Title: Name of the area covered.
- Scale: RF, Statement, and Linear Scale.
- Grid Reference: Explains the Eastings and Northings system for locating points.
- Contour Interval (VI): The vertical difference in height between successive contour lines. Stated explicitly (e.g., "Contour Interval 20 metres").
- Legend/Key: Explains the conventional signs and symbols used.
- Administrative Boundaries: Shows district, state boundaries if present.
- Magnetic Declination: Shows the difference between True North and Magnetic North for the year of survey.
- Publication Details: Year of survey, publication date, publishing authority (Survey of India).
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B. Conventional Signs and Symbols: Standardised symbols used to represent various features. Key categories include:
- Relief Features: Contours, Spot Heights ( .234), Bench Marks (BM 234.5), Triangulated Stations (∆ 456), Form Lines (broken lines, approximate height).
- Water Bodies: Rivers (perennial/non-perennial), streams, tanks (lined/unlined), wells (lined/unlined, brackish), springs, canals, dams, reservoirs. Blue colour is standard.
- Vegetation: Forests (reserved/protected, dense/open), scrubs, grasslands, orchards, plantations. Green colour often used for wooded areas.
- Transport & Communication: Roads (metalled/unmetalled, cart track, pack track, foot path), railways (broad/metre gauge, station), bridges, causeways, ferries, post office (PO), telegraph office (TO), police station (PS), Circuit House (CH), Dak Bungalow (DB). Red colour often used for roads and grids.
- Settlements: Villages, towns (huts - permanent/temporary), buildings, forts, temples, churches, mosques, tombs, graveyards. Red or black symbols.
- Boundaries: International, state, district, tehsil/taluk. Different line patterns.
- Other: Mines, quarries, kilns, windmills, electric lines.
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C. Representation of Relief: Primarily through Contours.
- Contours: Imaginary lines joining places having the same elevation above Mean Sea Level (MSL). Brown colour is standard.
- Contour Interval (VI): The constant vertical difference between consecutive contours. Smaller interval for flat terrain, larger for steep terrain.
- Index Contours: Every 5th contour is usually drawn thicker and numbered for easy reading.
- Characteristics of Contours:
- Widely spaced contours indicate gentle slope.
- Closely spaced contours indicate steep slope.
- Uniformly spaced contours indicate uniform slope.
- Contours never cross or merge (except in special cases like cliffs or waterfalls).
- Closed contours with decreasing height inwards represent a depression (lake, pond).
- Closed contours with increasing height inwards represent a hill or knoll.
- Contours cross valleys and ridges at right angles.
- V-shaped contours pointing uphill indicate a valley or re-entrant. The 'V' points towards higher ground.
- U-shaped or rounded contours pointing downhill indicate a ridge or spur. The 'U' points towards lower ground.
- Other Methods (shown on topo sheets): Spot Heights, Bench Marks, Triangulated Stations provide exact height at specific points. Hachures and Hill Shading are less common on modern SoI sheets but represent slope direction/steepness pictorially.
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D. Interpretation of Features:
- Landforms: Identify hills, valleys, plateaus, plains, ridges, spurs, cliffs, saddles/cols based on contour patterns.
- Drainage Patterns: Observe the network of rivers and streams. Common patterns and their implications:
- Dendritic: Tree-like branching, common on uniform, gentle slopes.
- Trellis: Parallel main streams with short tributaries joining at right angles, typical in folded C.
- Radial: Streams flowing outwards from a central high point (volcano, dome).
- Rectangular: Streams follow fault lines, joining at right angles.
- Centripetal: Streams flowing inwards into a depression or basin.
- Settlement Patterns: Observe the distribution and layout of settlements:
- Nucleated/Clustered: Buildings grouped closely together, often near resources or defensive sites.
- Dispersed/Scattered: Buildings spread out over a large area, common in agricultural regions or hilly terrain.
- Linear: Buildings arranged along a road, river, railway line, or coast.
- Land Use: Inferring activities based on symbols: cultivated areas (yellow wash), forests (green), orchards, wasteland (stippled patterns), mines, quarries.
- Transport & Communication: Analyse the network density and type (roads, railways) to understand accessibility and economic activity.
- Inter-relationships: The key is to connect different elements – how relief influences drainage, settlement, land use, and transport networks. For example, steep slopes might have forests and dispersed settlements, while flat valley bottoms might have agriculture, nucleated settlements, and major transport routes.
5. Importance for Exams
- Direct questions on definitions (contour, scale, RF).
- Identification of features based on conventional signs.
- Interpretation of contour patterns (slope, landforms like ridge/valley).
- Understanding the map numbering system.
- Calculating distances using the scale.
- Interpreting drainage and settlement patterns.
- Identifying land use from symbols and colours.
Multiple Choice Questions (MCQs)
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Topographical maps are considered 'large-scale' maps because they:
a) Cover a very large area of a country.
b) Show features in great detail with a relatively large Representative Fraction (RF).
c) Are primarily used for showing global climate patterns.
d) Use a very small Representative Fraction (RF). -
If the scale of a topographical map is given as 1:50,000, what does it mean?
a) 1 cm on the map represents 50,000 km on the ground.
b) 1 inch on the map represents 50,000 feet on the ground.
c) 1 unit on the map represents 50,000 of the same units on the ground.
d) 50,000 cm on the map represents 1 km on the ground. -
Imaginary lines on a topographical map connecting points of equal elevation above Mean Sea Level are called:
a) Isobars
b) Isotherms
c) Latitudes
d) Contours -
On a topographical map, contour lines that are very closely spaced indicate:
a) A gentle slope
b) A flat plain
c) A steep slope
d) A uniform slope -
The symbol 'BM 245.6' printed on a Survey of India topographical map represents:
a) A spot height of 245.6 metres.
b) A Bench Mark with an elevation of 245.6 metres above MSL.
c) A Triangulated Station at 245.6 metres elevation.
d) A boundary marker post number 245.6. -
In the Indian topographical map numbering system, a sheet marked '53 C' represents:
a) A Million Sheet covering 4° x 6°.
b) A Degree Sheet covering 1° x 1°.
c) A 1:50,000 scale sheet covering 15' x 15'.
d) A 1:25,000 scale sheet covering 7.5' x 7.5'. -
When contour lines form a 'V' shape, the apex of the 'V' generally points towards:
a) Lower elevation (indicating a ridge or spur)
b) Higher elevation (indicating a valley or re-entrant)
c) The North direction
d) A water body -
The vertical difference between two consecutive contour lines on a topographical map is known as:
a) Representative Fraction (RF)
b) Grid Interval
c) Contour Interval (VI)
d) Vertical Scale -
A settlement pattern where houses are built along a road, river, or railway line is best described as:
a) Nucleated
b) Dispersed
c) Radial
d) Linear -
A drainage pattern resembling the branches of a tree, typically developing on relatively uniform bedrock and gentle slopes, is called:
a) Trellis
b) Dendritic
c) Radial
d) Rectangular
Answer Key:
- b
- c
- d
- c
- b
- b
- b
- c
- d
- b
Make sure you practice reading actual topographical sheets alongside these notes. Pay close attention to the legend and the contour patterns. Good luck with your preparation!