Geography · Lesson 16

Practical geography 1: the map extract, scale, distance, area, grid references and bearings

JAMBWAECNECO

What the syllabus asks

JAMB: maps, scale and measurement of distances, areas, reduction and enlargement, directions and bearings. Builds on gg8 with a full worked map extract.

WAEC: WAEC/NECO Geography Paper 3, Question 1 (compulsory map reading, 25 marks): scale, measurement of distances, map reduction and enlargement, direction and bearing, area, grid references

NECO: WAEC/NECO Geography Paper 3, Question 1 (compulsory map reading, 25 marks): scale, measurement of distances, map reduction and enlargement, direction and bearing, area, grid references

What you will learn

Read marginal information and conventional signs on a topographical map.
Convert between RF, statement and linear scales.
Measure straight and curved distances and convert them to ground distances.
Calculate the effect of reduction and enlargement on lengths and areas.
Estimate areas by counting grid squares.
Give four- and six-figure grid references.
Describe directions and measure bearings and back bearings.
Allow for magnetic declination using marginal information.

Key points

Question 1 is compulsory and carries 25 marks; aim to finish it in 35 minutes.
Read the scale and contour interval in the margin before measuring.
At 1:50 000, centimetres ÷ 2 = kilometres.
Follow every bend of a route with string or a paper edge.
Halving the scale quarters the area on paper.
Count whole squares plus those half or more covered.
Grid references: eastings first; estimate tenths for six figures.
Bearings are clockwise from north, in three figures.
Back bearing: add or subtract 180°.
Show measurement, conversion and units for every answer.

Start here: Concept summary: what the map question demands

Question 1 of WAEC Geography Paper 3 (Elements of Practical and Physical Geography) is compulsory. It is built on a contoured topographical map extract, usually of a part of West Africa, and carries 25 of the paper’s 70 marks. The whole paper lasts 1 hour 50 minutes, you answer four of eight questions, and WAEC advises you to spend no more than 35 minutes on Question 1. NECO’s Geography paper follows the same syllabus content and a very similar map question; always obey the front page of your own paper. JAMB tests the same skills as multiple-choice items under “Practical Geography”: scale, distance, area, direction, bearing, gradient, cross-profiles, intervisibility and map interpretation.

This unit and the next two use one map extract throughout, the Oke-Ofa extract below. It is fictional: it was generated by computer from a mathematical model of the land surface, so every height, distance and bearing in these lessons has been calculated exactly and then checked. The extract is drawn at a scale of 1:50 000, the most common scale for West African survey maps used in the examination, with 1 km grid squares and a contour interval of 20 m.

Study it now for two minutes, exactly as you should in the examination hall. Notice the high, forested hill in the north-west with a trigonometrical station at 455 m, a lower rounded hill in the south-east (spot height 404 m), a small hill in the north (344 m), the River Ofa flowing from north-east to south-west with a left-bank tributary from the north-west hill, a tarred main road running west–east through the town of Oke-Ofa, a minor road running north from the town, a linear village (Agbede) along the main road, and scattered huts on the higher ground in the north-east.

The map question always mixes two kinds of task. Measurement tasks (this unit and unit gp2) have exact answers with small tolerances: scale conversion, distances, areas, grid references, directions, bearings, heights and gradients, and cross-sections. Interpretation tasks (unit gp3) ask you to describe and explain relief, drainage, settlement, communication and land use, and the relationships between them. Measurement marks are the easiest marks in the whole paper, because a careful student cannot be argued with. Your target is to collect every one of them quickly, leaving time for the interpretation parts.

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Practice questions

1. On a 1:50,000 map, 1 cm represents

0.5 km
5 km
50 m
1 km

Show answer

A: 0.5 km
50,000 cm = 500 m.

2. A distance of 4 cm on a 1:50,000 map is

20 km
200 m
4 km
2 km

Show answer

D: 2 km
4 × 0.5 km.

3. A map scale written as “1 cm to 0.5 km” is a

linear scale
grid scale
statement scale
representative fraction

Show answer

C: statement scale
Words state the scale.

4. A representative fraction of 1:50,000 means

the map is 50 km wide
1 unit on the map = 50,000 of the same units on the ground
1 cm = 50 km
1 km = 50,000 cm on the map

Show answer

B: 1 unit on the map = 50,000 of the same units on the ground
RF has no units.

5. Reducing a map to half its length scale changes 1:25,000 to

1:50,000
1:12,500
1:100,000
1:25,000

Show answer

A: 1:50,000
Scale denominator doubles.

Key words

Topographical map: A map showing relief and both natural and man-made features of an area.
Map extract: A section of a survey map printed for an examination.
Representative fraction: Scale written as a ratio with no units, e.g. 1:50 000.
Linear scale: A divided line showing ground distances; stays correct when a map is copied at a new size.
Conventional signs: Standard symbols used on survey maps.
Easting: A vertical grid line, numbered along the top and bottom of the map.
Northing: A horizontal grid line, numbered along the sides of the map.
Grid reference: Numbers locating a square (4 figures) or a point (6 figures).
Bearing: Angle measured clockwise from north, in three figures.
Back bearing: The reverse bearing; differs by 180°.
Magnetic declination: Angle between magnetic north and true or grid north.
Trigonometrical station: A survey point of known height, shown by a triangle.

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