It wasn’t until the 19th century that Ordnance Survey created “the first comprehensive, detailed picture of Britain”, says The Economist. Its original purpose was national defence: the country was facing “constant military threats” from Europe, and to see off invaders you have to “know the lie of your land”. Accordingly, the first OS maps produced, in 1801, covered the mouth of the River Thames: “the naval route to London and a highly vulnerable part of the country”. It was tough work: they were marching through remote countryside, carrying heavy equipment. The pace of the Industrial Revolution meant some maps were out of date “before they had been engraved onto copper plates for printing”.
Scotland was particularly tricky. Surveyors found themselves “encamped on a mountain for weeks waiting for the mist to break”. They could operate only in the spring and summer, which landowners hated because it “overlapped with deer-stalking season”. But the “slow, arduous, physical work” paid off: the final maps, of Orkney and Shetland, were published in 1882, eight decades after the project began. Things are very different today, with satellites that can “whip over Britain’s quarter of a million square kilometres every day”. But Ordnance Survey still employs more than 200 human surveyors. And they “still have to brave the British weather, rain or shine”.