On 18 April 1936, a small band of surveyors gathered around a concrete pillar in a field in Cold Ashby, Northamptonshire, to begin the retriangulation of Great Britain. The previous effort, from the early 1800s, had apparently become too out-dated to be useful.
Thus began the era of the trig pillar: those four-foot concrete obelisks that stand nobly on hilltops, helping map the country before the days of GPS. Revered today as “beloved features” of the British landscape, they now serve chiefly as selfie props for walkers, and as canvases for wannabe Banksies.
The principle behind triangulation is blissfully simple—measure angles from one known point to another and use a bit of clever maths to work out where another is. Naturally, this required over 6,500 trig pillars scattered across the land, because Britain is nothing if not thorough when being needlessly complex.
Atop each pillar would be placed a theodolite—essentially a fancy device for measuring angles. An observer would peer through this contraption for hours, squinting at distant lights and hoping the weather did not laugh in their faces. For the highest accuracy, they repeated this process until their souls left their bodies.
Before anything could be measured, however, something solid had to be built. Enter the pillar builders: rugged men of mystery who cheerfully carried sand, gravel, and cement up the highest hill in the area. They sometimes relied on horses and tractors, but above all, sheer bloody-mindedness to get the job done. The pillars had to be sunk three feet into the ground—any less and they had a tendency to fall over, which rather defeated the purpose.
The builders, naturally, were lauded for their “independence” and “determination,” which is another way of saying they were left to their own devices with shovels and bad weather. That most of their creations are still standing today is seen as a testament to their skill, or perhaps just an accident of fate.
In that inaugural summer of 1936 — it was naturally a summer job— the operation was split into three gallant teams. Each was headed by an “observer,” flanked by two assistants: a “booker,” presumably he who wrote things down, and a gopher, to go for this and go for that. Meanwhile, dotted about on distant hilltops were nine unfortunate souls known as lightkeepers, detached from the teams in every possible sense, left blinking into the void and waiting for someone to notice them.
These lightkeepers, armed with bicycles and heavy six-volt car batteries, climbed the mountains and cycled across the landscape chasing battery charges and flickering hope. They kept in touch via Morse code, just to ensure that even in the 1930s, the process retained the dignity and pace of Victorian Britain.
By 1962, the project was declared complete. Thus Britain’s mapping was modernised, in an age before satellites, but it took gangs of men, concrete pillars, and flashing lights to produce the maps I became so familiar with.
Source
Owen, Tim and Elaine Pilbeam. “Ordnance Survey—Map Makers to Britain since 1791”. Ordnance Survey. 1992.
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