OS Map Skills and Grid References
Ordnance Survey (OS) Maps
OS maps are detailed topographic maps of the UK that show both natural and human features. The two main scales used at GCSE are:
- 1:50,000 (Landranger) — 1 cm on the map = 500 m (0.5 km) on the ground; 2 cm = 1 km
- 1:25,000 (Explorer) — 1 cm on the map = 250 m on the ground; 4 cm = 1 km
Grid References
Four-Figure Grid References
Four-figure references identify a 1 km × 1 km grid square:
1. Read the easting (horizontal line) on the left side of the square: go along the corridor first
2. Read the northing (vertical line) on the bottom of the square: then go up the stairs
Memory aid: "Along the corridor and up the stairs" — always give the easting before the northing.
Example: A church in the square with easting 34 and northing 56 = 3456
Six-Figure Grid References
Six-figure references pinpoint a location to within 100 m × 100 m:
1. Read the easting line to the left of the feature: e.g. 34
2. Estimate how many tenths across the square the feature is: e.g. 7 → easting = 347
3. Read the northing line below the feature: e.g. 56
4. Estimate how many tenths up the square: e.g. 3 → northing = 563
5. Six-figure reference = 347563
Contour Lines
Contour lines join points of equal height above sea level. On 1:50,000 maps, contour lines are usually at 10-metre intervals.
Reading Contours
- Close together = steep slope
- Far apart = gentle slope or flat land
- V-shapes pointing uphill = a valley (river flows downhill in the direction the V points away from)
- V-shapes pointing downhill = a ridge or spur
- Concentric circles = a hill (height increases towards the centre)
- Concentric circles with tick marks = a depression or hollow
Spot Heights and Triangulation Pillars
- Spot heights (·374) — exact height at a specific point
- Triangulation pillars (△ 543) — fixed survey points, usually on hilltops
Measuring Distance
Straight-Line Distance
1. Place the straight edge of a piece of paper between two points on the map
2. Mark the start and end points on the paper
3. Place the paper along the scale bar to read off the distance
Curved Distance (e.g. along a road or river)
1. Use a piece of string or the edge of paper, pivoting at each bend
2. Straighten the string/paper and measure against the scale bar
3. Alternatively, use a map measurer (opisometer)
On a 1:50,000 map: each grid square is 1 km × 1 km, so the diagonal of one square = approximately 1.4 km
Drawing and Interpreting Cross Sections
A cross section shows the profile of the land between two points:
1. Place a strip of paper between the two points on the map
2. Mark where each contour line crosses the paper, noting the height
3. Transfer these marks to graph paper with height on the y-axis
4. Plot each height and join the dots with a smooth curve
Cross sections are useful for:
- Identifying hills, valleys, and flat areas between two points
- Assessing visibility (line of sight) between locations
- Understanding the landscape for route planning
Map Symbols
Key map symbols to know:
| Symbol | Feature |
|---|---|
| Blue lines | Rivers and streams |
| Blue area | Lake or reservoir |
| Green shading | Woodland (coniferous = ↑↑↑, deciduous = rounded) |
| Brown lines | Contour lines |
| Red/orange lines | A-roads and B-roads |
| Black dashed lines | Footpaths and bridleways |
| PH | Public house |
| Mus | Museum |
| PC | Public convenience |
| P | Parking |
| Church with spire (+) | Church with spire |
| Church with tower (□+) | Church with tower |
| ⛳ | Golf course |
Compass Directions
Use the 8-point compass for describing direction:
- N, NE, E, SE, S, SW, W, NW
- Always give the direction from one feature to another
Bearings — measured clockwise from north in degrees (000°–360°):
- North = 000°, East = 090°, South = 180°, West = 270°
- Use a protractor on the map aligned to the grid north
Describing Relief
When asked to describe the relief (shape of the land) from a map:
1. State the highest and lowest points with heights
2. Describe the general slope direction (e.g. "the land slopes from northeast to southwest")
3. Identify steep and gentle areas (using contour spacing)
4. Name specific features — valleys, ridges, flat areas, cliffs
5. Use evidence from the map — quote heights, grid references, contour patterns
Exam tip: Always use evidence from the map in your answers — quote grid references, heights, distances, and compass directions. Vague answers like "it is hilly" without specific data will lose marks.