On 18 April 1936 a group of surveyors gathered around a white concrete pillar in a field in Cold Ashby and began the retriangulation of Great Britain. That trig pillar is still standing 80 years on, along with thousands more around the country. We’re celebrating by sharing the story of the humble trig pillar, still much loved by walkers today, and giving you the chance to join our celebrations with The Trig Pillar Trail Challenge.
The shining (sometimes) white monoliths are now instantly recognised by any walker, or geography lover and have inspired many a trigbagger. They’re quintessentially British, and even made it onto Bill Bryson’s list of favourite British items in his 2015 book ‘The Road to Little Dribbling’. But what were they for? Now largely redundant, back in 1936, they formed a state-of-the-art network built to re-map Britain, dreamt up by Brigadier Martin Hotine. Responsible for the design, planning and implementation of the retriangulation, Hotine also designed the iconic trig pillar to provide a solid base for the theodolites used by the survey teams to improve the accuracy of their readings.
Some 6,500 were built, to be used for triangulation, the mathematical process that makes accurate map making possible. It works by determining the location of a point by measuring angles to it from known points at either end of a fixed baseline and in this case, those known points were the 6,500 trig pillars, across the country. OS surveying teams spent 26 years gathering measurements across Britain to create a highly accurate map of the country, but time and technologies have moved on enormously to the point where the traditional trig pillar is now obsolete in its original guise. They still act as a beacon for many an outdoors lover, but they no longer help shape our maps. Look out for tomorrow’s blog where we’ll share more detail on the history of the trig pillar, how they were built and used, the inner workings and much more.
Although 6,500+ trig pillars were built, hundreds have been lost to housing developments, farming, coastal erosion and other causes. The greatest source of information on trig pillars (and other Ordnance Survey surveying marks) is www.trigpointing.uk. Users on there regularly ‘bag’ trig pillars and take photos to track their condition.
While there are many trig-baggers out there, trig-bagger extraordinaire Rob Woodall completed his 14-year mission to bag all of Britain’s trig pillars last weekend in Fife. He’s bagged 6,190 trig pillars, a seriously impressive achievement. We joined his final bagging expedition and awarded him a mounted flush bracket to mark the moment. Look out for Thursday’s blog with more details on his final trig-bagging adventure.
We’d love you to get involved in the trig pillar birthday celebrations too and have put together The Trig Pillar Trail Challenge. Rob Woodall, our #GetOutside champions and some of us at OS, have nominated our favourite trig pillars around the country. Many of our champions have also put together walking, running or cycling routes for you to reach the trig pillars using OS Maps.
To celebrate the trig pillar and getting outside to explore Britain, if you take a photo of one, or with one, anywhere around the country, send us a photo on Twitter or Instagram using #TrigPillar80, and you could win a limited edition T-shirt.
The modern equivalent is the OS Net network of 110 Global Navigation Satellite System(GNSS) receivers. Our surveyors use OS Net and GNSS technology every day to instantly position new map detail to within a few centimetres. What took many hours at Cold Ashby in 1936 we can now do in seconds and to a far greater degree of accuracy. Find out more about our current surveying process later this week on the blog.
See the BBC gallery celebrating the 80th birthday of the trig pillar.