UK Trig Points
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.
|Tick List||Number of Trigs||Number Visited|
|Click each area for more trig details and the routes I used|
All My Trig Point Visits
You can see a full list of my trig points here: All Trigs by Year.
My profile on trigpointingUK also has the full list, along with all the logs I've added.
Trig Point Downloads for Memory Map v5
I've been using Memory Map to plan walks and to bag trigs for a few years now. The files below are the final evolution of several different attempts to create a useful Trig Point Overlay for Memory Map.
Due to the number of trig points, I've split the country into 12 regions - otherwise the file takes ages to load on my PC. Each file has broken the trig points down into Type categories (Pillars, Berntsens, Rivets etc) and I've used the icon set provided by Lord Elph. Each trig point is locked in place and each is accurate to 1m. Double clicking on the icon in Memory Map opens a link to that trig on the trigpointingUK website. The comment field includes the name of the trig point, it's type and it's condition.
|Click the image to download the file (you will need WinZip to unpack it), these were created in v5 of Memory Map, so you will need that version to load them.|
I've also created MM Overlay files for three of the most popular National Parks. These are the parks I'm currently trying to complete. If you need another area creating - perhaps your county or one of the other National Parks, drop me an email and I'll create it for you. You will need the latest version of Memory Map v5 to open these.
Trig Point Types
|Pillar: The classic trig point and a welcome sight for hill walkers everywhere! A concrete pillar about 4' high, with a flush bracket near the base and a circular plate on top with grooves for mounting a theodolite. Whilst most have fallen into disuse, about 184 of them are currently used in the Passive Station network.|
|Vanessa Pillar: A cylindrical pillar, mainly seen on high mountains tops where they were easier to construct, but also found occasionally at low levels.|
|FBM - Fundamental Benchmark: An underground chamber topped with a short granite pillar. The pillar contains an easily accessible height reference point, but the accurately measured level is underground where it is less likely to be disturbed. There are approximately 200 FBMs across the country and whilst many have fallen into disuse, about 80 have been incorporated into the National GPS Network as Passive Stations.|
|Active Station: There are active stations sited at about 30 locations around the country. These are GPS receivers which constantly log their readings (known as Rinex data) on the Ordnance Survey website. This allows a very high level of positional accuracy to be achieved, without the need to physically occupy one of the Passive Stations.|
|Cannon: A very rare and elusive pillar - only 3 recorded in the database, taking their name from the distinctive cannon shape.|
|Concrete Ring: An unusual and difficult to spot monument, another rare type with only 10 recorded in the database.|