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To follow a long-distance route with an Ordnance Survey map, choose the right map sheets, learn the legend and contours, locate yourself with grid references, and check your position at regular landmarks. Use a compass bearing as an aid—not as a substitute for checking the mapped path and the ground around you.
Choose map sheets that cover the whole route
Ordnance Survey (OS) offers two paper map scales that suit different needs. An Explorer map gives more detail; a Landranger map covers a wider area on each sheet but shows less detail. A long-distance trail may cross several sheets, so check the sheet index against the route rather than assuming one map will cover it. [OS map ranges]
| Map range | Scale | What it suits | Map distance |
|---|---|---|---|
| Explorer | 1:25,000 | Detailed walking information, including footpaths, rights of way, open-access land and vegetation. | 4 cm represents 1 km; 1 mm represents 25 m. |
| Landranger | 1:50,000 | Wider coverage with less detail, often useful for longer routes. | 2 cm represents 1 km; 1 mm represents 50 m. |
These scales describe map distance, not the distance you will walk: bends, climbs and descents add ground distance. For a walking route where path detail matters, Explorer is the more detailed choice; Landranger trades some detail for broader coverage.
Decode the map before setting out
Start with the map’s legend, or key. OS maps use colours, symbols and line styles to represent landscape features; the key explains what they mean. Find the route and note the features you can use to recognise where you are, such as path junctions, roads, streams, buildings and access land. A map simplifies the landscape, so navigation depends on comparing it with what you can actually see.
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- Trace the route across the map and mark the sheet changes if it crosses more than one map.
- Identify prominent junctions, streams, ridges and other useful checkpoints.
- Check the legend for symbols you expect to encounter, including paths and terrain features.
Use grid references to locate yourself
OS National Grid lines divide the map into kilometre squares. Read a reference in two stages: eastings first, from left to right, then northings, from bottom to top. The mnemonic “along the corridor, then up the stairs” captures the order.
A four-figure grid reference identifies a kilometre square. More figures give a more precise position within that square. Use references to describe your location and to create repeatable checkpoints along the route; they are especially useful when you need to communicate where you are.
Read contours to judge the terrain
Contour lines join points at the same height, and their labels show height above sea level. Lines spaced far apart indicate a gentler slope; lines close together indicate steeper ground. Spot heights and symbols for features such as cliffs, scree and streams add context to the shape of the land.
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Do not assume the straightest line is the easiest, quickest or safest way through rough or mountainous terrain. Consider the distance, slope, weather, equipment and the fitness of the walkers. Following contours can avoid some steep climbs, but reassess the planned line if the terrain or conditions make it unsuitable.
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- South West CP
- South West Coast Path (National Trail)
- Cornwall
- Falmouth
- Helston
Keep checking your position as you walk
Measure the map distance to your next checkpoint with the scale or a compass ruler, then compare the expected distance with the ground features you encounter. Paths, junctions, streams and ridges can all help confirm that you are progressing as planned. A map’s straight-line distance does not account for the route’s bends or the extra distance caused by sloping terrain.
If travelling on a bearing, plan closer checkpoints—typically 500 to 1,000 metres apart, depending on terrain. Direction errors accumulate over distance, while pacing can become unreliable on difficult ground. You can also drift when traversing a slope, so check the map and nearby features rather than relying on a single estimate.
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Take and follow a compass bearing carefully
- Place the compass baseplate on the map, with its edge running from your current position to your destination. Point the direction-of-travel arrow toward the destination.
- Turn the compass housing so its orienting lines align with the map’s north-south grid lines.
- Account for the magnetic variation shown in the map legend. Variation changes over time, so use the correction on the current map rather than relying on one remembered from another map or walk.
- Keep the compass away from nearby iron and steel objects, which can affect its reading.
- While walking, aim for a visible landmark along the bearing, then check your progress against nearby map features and the next checkpoint.
A bearing is one navigation aid, not permission to ignore a mapped path or continue when the ground does not match the map. If the terrain is unexpected, stop and work out your position again before proceeding.
Check route conditions separately
A map-reading method cannot establish whether a particular trail is currently open, passable or suitable for your plans. Access status, weather, transport and route conditions depend on the trail and the date of your walk. Check current local and official information before setting out, and adjust plans to the conditions you find.
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