UK Trig Points

Trig point on Stanage Edge
Trig point on Stanage Edge

Trig points, or to use their official name, triangulation pillars are concrete or stone pillars about 4 feet high which were used by the Ordnance Survey to provide an accurate picture of the shape of the British Isles. There are approximately 6500 of these pillars spread all across the mainland and islands of the UK. They are generally located at the highest point in an area, such that there is a clear view from one pillar to another. By fixing a theodolite to the top of the pillar an accurate bearing to one or more nearby trigpoints can be taken, in a process known as triangulation.

In 1935, the then Director General of the Ordnance Survey, Major-General Malcolm MacLeod, started the retriangulation of Great Britain, an immense task which involved the building of several thousand trig points. The results of the retriangulation were then used to create the British National Grid reference system which would be the basis of the Ordnance Survey’s new maps. These are still some of the best maps produced in the world today, what lucky people we British walkers are 🙂

At the start of my walking career I paid little heed to these concrete pillars, other than recognising that they marked the end of another exhausting climb up some hill or other. After seeing a few of them though I started to wonder how many there were and rather than stumbling across them accidentally I started to seek them out. This marked the start of my trig bagging exercise. Trig bagging is a little publicised, but surprisingly much practiced activity. We have several web sites devoted to the “sport”, the best one (in my opinion) being trigpointingUK. Where you can see how many trig points there are across the country and who has visited them recently. On that site my name is also Lone Walker.

As well as the traditional concrete pillars, there are a huge number of other Ordnance Survey triangulation devices and monuments, many of which are buried under a few inches of topsoil. After a few years of trying to collect all the OS devices in an area I found the underground ones to be particularly frustrating and time consuming, so I have decided to concentrate on bagging only monuments above ground, i.e. Pillars and the like. You can see the trig types I am currently collecting at the bottom of this page. The next table shows my progress against the collections of trig points I am currently working on.

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