Key Stage 3 geography · Geographical skills and fieldwork

KS3 OS maps: grid references, scale and contours

Ordnance Survey (OS) maps are the detailed maps of Great Britain that schools use to teach map-reading. In Key Stage 3, students build on primary-school skills to give six-figure grid references, measure distances using scale, and read contour lines to describe height, slope and landforms. These are practical skills that are used on fieldwork days and in exam questions, and they improve with real practice outdoors.

OS maps: grid references, scale and contours, explained

A grid of blue lines covers an OS map, dividing it into squares each representing 1 kilometre by 1 kilometre. Each line has a two-digit number printed at the edge. A four-figure grid reference identifies a whole square: first the number of the line on the left of the square (the eastings, reading along the bottom), then the number of the line at the bottom of the square (the northings, reading up the side). The memory aid is “along the corridor and up the stairs”. At KS3 students go further, imagining each square divided into tenths to give a six-figure reference that pinpoints a feature to within 100 metres.

Scale links the map to the real world. A scale of 1:50,000 means that 1 cm on the map represents 50,000 cm on the ground, which is 500 metres, so 2 cm is 1 kilometre. A scale of 1:25,000 shows more detail, with 4 cm to 1 kilometre. Students measure straight-line distances with a ruler and convert them. For winding paths or rivers, they lay a piece of string along the route, straighten it and measure that. They also compare maps at different scales and explain which is better for a particular job, such as planning a walk or a town trail.

Contour lines are the key to relief, which means the shape of the land. Each contour joins points of equal height above sea level, and the vertical gap between neighbouring contours (the contour interval) is given on the map; it is usually 10 metres on 1:50,000 maps and 5 or 10 metres on 1:25,000 maps, so students are taught to check. Lines close together mean steep slopes, lines far apart mean gentle ones, and rings getting smaller towards the middle usually mean a hill. Valleys and spurs have distinctive patterns: contours bend uphill in a valley and point downhill on a ridge or spur. Spot heights and trig points give exact heights at certain places.

Students are also expected to combine information. They might describe the route of a walk, noting where it climbs and descends; identify what a settlement’s site offers, such as flat land near a river crossing; draw a cross-section showing a slope in profile; match an OS map to an aerial photograph of the same area; or estimate the gradient of a path by dividing the height gained by the horizontal distance. These tasks bring together grid references, scale, symbols and contours, and they are practised in the classroom and on fieldwork.

A good deal of KS3 geography is now done on screen with digital maps, but many schools still teach with paper OS maps because they make students think about what the symbols and lines mean. The same skills are needed in GCSE geography, where map-reading is assessed again, and they are also a useful foundation for outdoor activities such as hill walking and orienteering.

Words your child will hear

Grid reference: A set of numbers that locates a place on a map using eastings and northings.
Easting: A grid line running up the map, read along the bottom; always given first.
Northing: A grid line running across the map, read up the side; always given second.
Scale: The relationship between distance on the map and distance on the ground, such as 1:50,000.
Contour line: A line on the map joining places of the same height above sea level.
Relief: The shape of the land, including its height and steepness.
Spot height: A number on the map giving the exact height of a point above sea level.

What the National Curriculum says

In Key Stage 3, pupils should be taught to:

Interpret Ordnance Survey maps in the classroom and the field, including using grid references and scale, topographical and other thematic mapping, and aerial and satellite photographs
Build on their knowledge of globes, maps and atlases, and apply and develop this knowledge routinely in the classroom and in the field

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

A model answer: grid reference, distance and slope

A map has a scale of 1:50,000. A farm lies inside the grid square whose bottom-left corner is at easting 34 and northing 35, six-tenths of the way across the square and seven-tenths of the way up. Give its six-figure grid reference. A hilltop trig point is 4 cm away on the map, at 180 m, while the farm is at 80 m. How far apart are they, and how steep is the slope?

Write the eastings first. The square starts at easting 34. The farm is six-tenths of the way across, so the third figure is 6. The eastings part is 346.
Then the northings. The square starts at northing 35 and the farm is seven-tenths up, so the final figure is 7. The northings part is 357. The six-figure grid reference is 346357.
```
Eastings:  34 + 6 tenths = 346
Northings: 35 + 7 tenths = 357
Reference: 346357
```
Convert the map distance using the scale. At 1:50,000, 1 cm represents 500 m. So 4 cm represents 4 × 500 = 2,000 m, which is 2 km.
```
1 cm = 500 m
4 cm = 4 × 500 = 2,000 m = 2 km
```
Work out the height gained: 180 m − 80 m = 100 m. The average gradient is the height gained divided by the distance: 100 ÷ 2,000 = 1 ÷ 20, so about 1 in 20.
```
180 − 80 = 100 m
100 ÷ 2,000 = 1/20
```
Finish with a short description using the evidence. A climb of 100 m over 2 km is a gentle, steady slope overall, but contours packed close together just below the trig point would show a steeper final section.

The farm is at grid reference 346357. The trig point is 2 km away, and the land rises 100 m over that distance, an average gradient of 1 in 20. The slope is gentle overall, though contours close together near the summit would show where it steepens.

Common mistakes and how to help

Giving the northings before the eastings

Students often read the map from the top or the side first, or simply forget the order.

What helps: Say “along the corridor and up the stairs” aloud every time. The first figures are always along the bottom of the map.

Reading a six-figure reference using the corner of the square rather than the position inside it

Students find the square correctly but give the third and sixth figures as 0 or guess them.

What helps: Use a card or ruler to measure the tenths. A feature halfway across a square has a 5 as its third figure.

Measuring distances and forgetting to convert with the scale

The ruler gives centimetres, and writing down the number feels like the answer.

What helps: Write the scale conversion at the side before measuring: “1 cm = 500 m”. Then check the answer is sensible for the place.

Thinking contours show the sides of a hill and not the height

They look like outlines drawn around hills.

What helps: Imagine slicing the hill at regular heights, like slicing a cake horizontally. Each slice’s edge is a contour, which is why close lines mean steep ground.

How to help at home

Take an OS map on a walk. Use a map for a short, safe walk in a park or familiar countryside, with an adult. Ask your teenager to find where you are, name the next feature and say whether the path is about to climb.
Give grid references for the house. Find your home on a local map and ask for the four-figure and then the six-figure reference of the nearest church, school or station. Compare answers to check.
Measure the journey. Choose two places on a map and estimate the distance between them using the scale, then check against a trip or a walk. It teaches how to convert and spot errors.
Build a contour model. Use modelling clay or layers of cardboard to make a small hill, then draw its outline from above at each height. This is the best way to see why contours look as they do.
Practise the gradient maths. Pick a hill from a map and work out the average gradient between two spot heights. Dividing height by distance links geography to maths and appears in exam questions.

Builds on

Key Stage 2: Atlases, globes and digital maps
Key Stage 2: Compass points and grid references
Key Stage 2: Ordnance Survey map symbols
Key Stage 2: Fieldwork: observe and measure
Key Stage 2: Fieldwork: presenting findings