Elements of a Map
Senior 1 · Geography
Elements of a Map
Lesson 3 of 4
25 min
A pilot flying from Kigali to Musanze, a surveyor marking a land plot and a rescue team looking for a lost hiker in Nyungwe all need two things: the direction to go in, and a way to name an exact place. On a map, direction is given by compass points or bearings, and place by a grid reference.
Figure 1. The points of the compass and their bearings, measured clockwise from north.
The four cardinal points are north, east, south and west. Halfway between them are the four intercardinal points: north-east, south-east, south-west and north-west. Halfway again gives the 16-point compass, such as north-north-east (NNE), which is between N and NE.
Definition
Compass bearing: the direction of one place from another, given as an angle measured clockwise from north, in degrees, and always written with three figures (000° to 360°). Example: east is 090°, south-west is 225°.
Worked example
Worked example 1: the bearing of Musanze from Kigali (Figure 2)
Step 1 On the map, draw a straight line from Kigali (the place you are measuring from) to Musanze.
Step 2 Draw a north line through Kigali, parallel to the grid lines that run north.
Step 3 Place the protractor's centre on Kigali with 0° on the north line. Musanze lies west of north, so measure the small angle between the north line and the Musanze line: .
Step 4 A bearing turns clockwise, so
Answer. The bearing of Musanze from Kigali is 316°, which is between north-west (315°) and north-north-west.
Figure 2. The bearing of Musanze from Kigali is 316°: turn clockwise from north until you face Musanze.
Worked example 2: the return journey (back bearing)
What is the bearing of Kigali from Musanze? Going back means facing the opposite way, which is a turn of .
Rule: if the bearing is more than 180°, subtract 180°; if it is less than 180°, add 180°. So the bearing of Kigali from Musanze is 136° (south-east).
Warning
"From" matters. "The bearing of B from A" means you stand at A. Put the protractor on A, not B. Mixing them up gives the back bearing, which is wrong by 180°.
Topographic maps are covered by a grid of numbered lines. Lines running up the map are eastings: their numbers increase towards the east (to the right). Lines running across are northings: their numbers increase towards the north (up the map). On a 1:50,000 map the lines are 2 cm apart, so each square is 1 km by 1 km.
Figure 3. Practice map of an imaginary area (scale 1:50,000, one grid square = 1 km). The school's square is divided into tenths.
Definition
Grid reference: a set of numbers that gives the position of a place on a map by using the grid lines: the easting first, then the northing. A four-figure reference names a grid square; a six-figure reference names a point within the square, to the nearest tenth. Example: in Figure 3 the church is in square 2164.
Worked example 3: four-figure reference of a square
The church in Figure 3 is in the square whose bottom-left corner is where easting 21 meets northing 64. Give the easting then the northing: 2164.
Always use the lines at the bottom-left (south-west) corner of the square.
Worked example 4: six-figure reference of the school
Step 1. Easting. The school is east of line 23. Divide the square into ten (the red ticks): the school is 4 tenths of the way to line 24. Easting = 23 and 4 = 234.
Step 2. Northing. The school is north of line 62, 7 tenths of the way to line 63. Northing = 62 and 7 = 627.
Answer. Grid reference 234627.
Tip
"Along the corridor, then up the stairs." Read eastings (along the bottom) first, then northings (up the side). For bearings: "Naughty Elephants Squirt Water" gives N, E, S, W going clockwise.
Worked example 5: bearing and distance on the grid map
Find the bearing and the straight-line distance of the health centre from the school in Figure 3.
Bearing. The health centre is 0.9 of a square east and 1.5 squares south of the school, so it is south-east of it. Measured with a protractor from the school's north line, the angle is 149°.
Distance. The line measures 1.75 grid squares. Each square is 1 km, so the distance is about 1.75 km. (On the printed 1:50,000 map the line would be 3.5 cm: cm = 1.75 km.)
Important
Case study: the grid in real life
The grid idea is used far beyond the classroom. Rwanda's land register gives every plot of land its own identification number and records its boundary on a map, so that ownership can be checked. Ambulance services and delivery riders use the coordinates from a phone's GPS, which is a grid (latitude and longitude) covering the whole Earth. You will meet latitude and longitude in Unit 3.
How to take a 6-figure grid reference, with Steve Backshall and Ordnance Survey (2 min). Watch how the square is split into tenths before the numbers are read.
A friend tells you: "The market is at grid reference 6022." Using Figure 3, explain what mistake your friend has made and give the correct four-figure reference.
Practice
Remember
Sources and credits
Written by Ganzaa: the lesson text, compass rose, bearing diagram, practice map, worked examples and practice. The Kigali to Musanze bearing was calculated from the towns' latitude and longitude.
