Ordnance Survey is Britain’s national mapping agency, and its paper maps are the standard equipment of anyone walking in the British countryside. The name puzzles visitors: ordnance means artillery, and the organisation began as a military exercise.
The Jacobite origin
After the 1745 rising and the defeat of the Jacobites at Culloden, the British army discovered it had no usable maps of the Scottish Highlands — a serious problem when trying to control the region. A military survey of Scotland was ordered under William Roy, and it was so evidently useful that the principle was extended.
The Board of Ordnance, which handled artillery and fortifications, was given the job of mapping the south coast of England in 1791, with invasion by revolutionary France in prospect. That date is taken as the founding of Ordnance Survey, and the first one-inch map, of Kent, appeared in 1801.
The maps that matter
Two series are used by walkers, and knowing which is which is genuinely useful:
- Explorer — orange covers, scale 1:25,000. Four centimetres to the kilometre. Shows individual field boundaries, walls, stiles and paths. This is the one for walking.
- Landranger — pink covers, scale 1:50,000. Covers more ground in less detail. Better for cycling, driving and planning.
Both show public rights of way in green or magenta, which is the feature that makes them indispensable in a country where you may legally walk across private farmland. See the countryside.
The National Grid
Britain is divided into 100-kilometre squares each identified by two letters, subdivided by numbers. A six-figure grid reference such as SD 812 730 locates a point to within 100 metres; eight figures gets you to ten.
Giving a grid reference is the standard way to report a position to mountain rescue, and being able to read one off a map is a basic skill of British hillwalking.
Trig pillars
The concrete pillars found on hilltops across Britain — around 6,500 were built from 1936 for the retriangulation of Great Britain, each sited so that at least two others were visible from it, allowing the country to be surveyed by triangle.
They are obsolete now, superseded by satellite positioning, and OS maintains only a small number. But they remain a fixture of British summits, and “trig bagging” — visiting and photographing them — is a recognised hobby with its own database of every pillar’s condition.
The symbols
OS map legends run to several hundred symbols, and some are genuinely charming: a distinction between deciduous and coniferous woodland, separate symbols for a church with a tower and a church with a spire, and individual marks for a lighthouse, a windmill, a golf course and a mast.
The church distinction exists for a practical reason — towers and spires look different from a distance and are useful for taking a bearing.
Now
OS is a government-owned company, and most of its revenue comes from licensing data to government, utilities, emergency services and businesses rather than from selling maps. The OS Maps app puts the full mapping on a phone.
The paper maps nonetheless remain standard advice for anyone on the hills, for the reason every mountain rescue team repeats: a map does not run out of battery, and it works in the wet.