triangulation – The Map Room

Heritage Group Seeks Listed Status for First and Last Trig Pillars

Published on 21 April 202621 April 2026 by Jonathan Crowe

The Twentieth Century Society, a heritage group that campaigns to preserve 20th-century British buildings, is trying to get Grade II-listed status for the first and last trig pillars of the Retriangulation of Great Britain, which took place between 1935 and 1962. Many of the Retriangulation’s 6,500 pillars were adopted by local groups after the Ordnance Survey backed down from the proposal to remove them in 1992. Guardian coverage. [Derek Lyons]

Ten years ago: The Trig Pillar at 80.

An Ordnance Survey Roundup

Published on 6 June 2016 by Jonathan Crowe

Scottish newspaper The Courier has a somewhat belated piece on the 80th anniversary of the Ordnance Survey’s trig pillars.

Concomitant with the Survey’s map of Mars was a competition to design a map symbol to represent landing sites. The winner has been announced: the OS will use Paul Marsh’s symbol, which incorporates the Mars symbol with landing gear, on its Mars maps in the future.

The Trig Pillar at 80

Published on 18 April 2016 by Jonathan Crowe

andrew-trig-pillar — Blencathra From Skiddaw Trig Pillar. OS BM S1543. Photo by Andrew (CC licence).

The Ordnance Survey are marking the 80th anniversary of the Retriangulation of Great Britain, which began on this day in 1936. More from BBC News. Events include the Trig Pillar Trail Challenge, which invites people to post pictures to social media of one of 25 selected trig (triangulation) pillars (the #TrigPillar80 hashtag is very busy this morning). There are Flickr galleries of various trig pillars from Flickr user Andrew (who took the one above in 2013) and (of course) the Ordnance Survey.