Home / Aspects Of Dartmoor / Trig Points

Trig Points

Trig Points

Dartmoor is no different to anywhere else in the country as far as trig points are concerned – they appear everywhere. But there seems to be a growing hobby of visiting as many of these ‘modern menhirs’ as possible and so this page is for anybody who wanted to call on the Dartmoor ones.

The first trig points began appearing in 1935, their purpose was to enable the accurate re-mapping of Great Britain. This was done by a method known as triangulation which was devised by Martin Hotine, a mathematics expert and cartographer. Once all the trig points were sited it was always possible to see at least two other trig points when stood by one. This mean that it was possible to triangulate the measurements between the lines-of sight of other points thus arriving at a grid of triangles. Once these were measured against a  base line it provided, what for the times, was a very accurate measuring system for the whole country.

Trig Points are short, square based pyramids, usually white but that depends on weathering and how many animals have used it as a rubbing post. On the top of the trig is a brass plate with a depression in the middle and three hooped arms. This was used to fix the theodolite when the surveyors were taking their measurements. Another brass plate was fixed to the side on which was marked, O/S/B/M – (Ordnance Survey Bench Mark), and the reference number for the trig point.

In this modern age of GPS, digital mapping, and laser measuring the trig point’s role has become obsolete which means many of them are being taken away. This in many respects is sad because not only are we losing a familiar landscape feature we are losing an excellent navigational aid. Those who letterbox will soon tell you that there are hundreds of letterbox sites that have trig point bearings in their clues.

Trig Points

Hambledon Trig Point.

In 1992 a scheme was launched to ‘adopt a trig pillar’ whereby anybody could adopt a trig point as long as they maintained it and had the landowners consent which many walking clubs and individuals did. However this still has not stopped the removal of many of the famous land marks.

Today, on Dartmoor there are around about 32 trig points still stood up on the high tors and moors and are listed along with their height in feet and the OS grid reference below:

 

Location Height OS Grid Ref. Location Height OS Grid Ref.
Yes tor 2,019 58085 90151   Butterdon 1,189 65530 58643
Great Links tor 1,896 55080 86758   Ringmoor Down 1,148 57527 66745
Cosdon Hill 1,804 63610 91501   Bel tor 1,143 69640 72983
Hameldon tor 1,727 70315 80568   East Hill 1,137 59577 93893
Ryder’s Hill 1,687 65975 69058   Cranbrook Castle 1,098 73863 88913
North Hessary tor 1,685 57872 74213   Westcott 1,092 78790 86376
Lee Moor 1,611 60255 64498   Brent Hill 1,022 70303 61698
Rippon tor 1,537 74655 75566   Shaugh Moor 988 55893 63208
Three Barrows 1,508 65320 62580   Wallaford Down 952 70558 65885
Cramber tor 1,455 59237 71210   Cranbrook – New Site 944 74200 88801
Cox tor 1,438 53070 76176   Tor Down 889 69515 91838
Sourton tor 1,431 54330 89818   Chericombe Head 844 82058 80788
Easdon tor 1,426 72945 82311   Higher Bowden 682 63020 57233
Bellever tor 1,406 64463 76436   Roborough Down 645 50605 64126
Penn Beacon 1,395 59940 62933        
Meldon Hill 1,274 69568 86103   Unconfirmed    
Gibbet Hill 1,153 50310 81141   Blackingstone Quarry 1,044 78365 85846

 

 

With the exception of Cranbrook Castle all the trig points are still shown on the Ordnance Survey maps. There is currently a series of letterboxes on the moor with a stamp for each trig point which makes for a very interesting collection.

 

Trig Points

About Tim Sandles

Tim Sandles is the founder of Legendary Dartmoor

Check Also

Rustlers2

Rustlers on the Moor

Mention the word rustlers and thrilling images of masked cowboys running off herds of cattle …

Leave a Reply

Your email address will not be published. Required fields are marked *