Mapping Skills — Class 9 Social Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 9 Social Science, Geography — Chapter 7. Reading and understanding maps.
1. About this lesson
This chapter teaches the essential skills of reading, interpreting, and drawing maps — including types of maps, scale, directions, conventional symbols, and contours.
2. What is a Map?
A map is a representation of the Earth's surface or a part of it drawn to scale on a flat surface.
Types of Maps
| Type | Purpose |
|---|---|
| Physical / Relief Map | Shows natural features — mountains, rivers, plateaus, plains |
| Political Map | Shows boundaries — countries, states, districts |
| Thematic Map | Shows specific themes — population, rainfall, crops, industries |
| Topographic Map | Detailed map showing both natural and man-made features using symbols and contours |
3. Map Scale
- Scale: The ratio between the distance on the map and the corresponding distance on the ground.
Types of Scale
| Type | Example |
|---|---|
| Statement Scale | 1 cm = 10 km |
| Representative Fraction (RF) | 1:1,000,000 |
| Linear / Graphical Scale | A drawn line divided into equal parts |
- Large-scale maps: Show small area in great detail (e.g., city map, 1:10,000).
- Small-scale maps: Show large area with less detail (e.g., world map, 1:100,000,000).
4. Directions
- Cardinal Points: North (N), South (S), East (E), West (W).
- Intermediate Points: NE, NW, SE, SW.
- Maps usually have an arrow pointing North.
- Compass: Instrument to find directions. The magnetic needle points towards the magnetic north.
5. Conventional Symbols
- Standard symbols used on maps to represent features.
- Colours: Blue (water bodies), Green (forests/vegetation), Brown (contours/relief), Red (roads, settlements), Yellow (cultivated land).
- Common symbols: ⛫ (church), 🏥 (hospital), ✈ (airport), —·—·— (railway), PO (post office).
6. Contour Lines
- Contour lines: Lines joining places of equal height above mean sea level.
- Closely spaced contours → steep slope.
- Widely spaced contours → gentle slope.
- Uniformly spaced → uniform slope.
Landforms represented by contours
| Landform | Contour Pattern |
|---|---|
| Hill | Concentric closed contours; values increase towards centre |
| Plateau | Widely spaced contours at top with steep sides |
| Valley | V-shaped contours; V points upstream (towards higher elevation) |
| Ridge | U-shaped contours; U points downstream |
| Saddle / Pass | Low point between two hills |
| Cliff | Contours merge/touch |
7. Worked examples
Example 1. If 1 cm on map = 5 km on ground, what is the RF scale? 1:500,000 (5 km = 500,000 cm).
Example 2. Closely spaced contours indicate what? Steep slope.
Example 3. How many satellites make up GPS? 24 satellites.
8. Book-back questions (Samacheer Kalvi)
I. Choose the best answer
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The new phase in topographical surveying in the 20th century is — (a) toposheets / (b) aerial photography / (c) maps / (d) satellite imagery. Ans: (d) satellite imagery.
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______ indicates the purpose or theme of the map — (a) Title / (b) Scale / (c) Direction / (d) Legend. Ans: (a) Title.
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Standard symbols used in maps to convey a definite meaning are called — (a) conventional signs and symbols / (b) coordinates / (c) grid references / (d) directions. Ans: (a) conventional signs and symbols.
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Which map shows a very large area with less detail? — (a) Large scale / (b) Thematic / (c) Physical / (d) Small scale. Ans: (d) Small scale.
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GPS consists of a constellation of ______ satellites — (a) 7 / (b) 24 / (c) 32 / (d) 64. Ans: (b) 24.
II. Match the following
| Column A | Column B |
|---|---|
| The art and science of mapping | e. Cartography |
| Thematic mapping | d. Political map |
| Actual shape of the earth | b. Geoid |
| A satellite | c. Inmarsat |
| NAVSTAR | a. USA |
III. Assertion and Reason
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A: The points at which the vertical and horizontal lines of the grid intersect are called coordinates. R: The lines running horizontally and vertically are called Northings and Eastings respectively. — (a) Both A and R are true; R explains A.
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A: The legend of a map does not help us understand the information in a map. R: It is usually placed at the left or right corner at the bottom of the map. — (a) A is false; R is true. (A is false — the legend DOES help us understand map information.)
IV. Answer in brief
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Name the different methods to represent the Earth. — Three methods: (1) Projection on the surface of a cylinder, (2) Projection onto the surface of a cone, (3) Projection directly onto a flat plane (planar/zenithal/azimuthal).
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What is a map? — A basic tool of a geographer. It illustrates the Earth's surface clearly through drawings, words, and symbols. A map is a location guide.
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What are the three components of a map? — Title, Scale, and Directions.
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The distance between two cities A and B is 5 km. It is represented by a line of 5 cm on the map. Calculate the RF. — Representative Fraction (R.F.) = Distance on map / Distance on ground = 5 cm / 5 km = 5 cm / 500,000 cm = 1:100,000.
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Mention a few surveying instruments. — Chain, Prismatic compass, Plane table, Dumpy level, Abney level, Clinometer, Theodolite, Total Station, and GNSS.
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Define remote sensing. — Remote sensing refers to the observation and measurement of earthly objects without touching them.
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What are Northings and Eastings? — Northings are horizontal grid lines (measured northwards); Eastings are vertical grid lines (measured eastwards).
V. Answer in detail
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Explain the types of maps based on scale. — Large-scale maps show small areas with great detail (e.g., cadastral maps, city plans). Small-scale maps show large areas with less detail (e.g., atlas maps, wall maps).
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Describe the essential elements of a map. — Title (purpose/theme), Scale (ratio of map distance to ground distance), Direction (North arrow), Legend/Key (explains symbols), Grid/Coordinates (location reference), and Conventional Signs & Symbols.
9. Common mistakes
- Mistake: Large-scale map shows a large area. Fix: Large-scale maps show a small area in detail. Small-scale maps show large areas with less detail.
- Mistake: Contour lines cross each other. Fix: Contour lines never cross each other (except at a cliff/overhang).
- Mistake: V of contour points downstream in a valley. Fix: In a valley, the V of contours points upstream (towards higher ground).
9. Quick revision
- Geography Ch 7 · Mapping Skills.
- Map types: Physical, Political, Thematic, Topographic.
- Scale: Statement (1 cm = 10 km), RF (1:1,000,000), Linear (graphical).
- Directions: 4 cardinal (N, S, E, W), 4 intermediate (NE, NW, SE, SW).
- Symbols: Standard colours — blue (water), green (forests), brown (contours), red (roads).
- Contours: lines of equal height. Close = steep, wide = gentle. Hill (concentric closed), Valley (V upstream), Ridge (V downstream).
