OS Triangulation Points

In the 1700’s the first baseline for triangulation was measure on Hounslow Heath. It first used wooden then iron and finally glass rods for better accuracy to measure the baseline of the first triangle. Subsequent triangulations formed new baselines, then in 1936 a whole new system of triangulation was developed by Ordnance Survey along with a whole new set of markers on the ground for the triangulation points.

The last triangulation of Britain took place between 1935 and 1962 with the now familiar triangulation pillar being used for the first time. Along with the pillars there were several other types of markers employed for the survey points.

Buildings were often used, especially ones which would not probably be pulled down in the future, churches were a favourite, Bakewell was one, as was the Hunting Tower and its flagstaff on the Chatsworth estate.

Fundamental Benchmarks were the cornerstone of the whole system, these were protected by iron fencing. The FBM as they were known were seated on bedrock and were used as definitive levelling points as the one on the Mortimer Road on Broomhead Moor.

Surface Blocks like the one at Hollingworth Head, there is also one near Big Moor formed part of the triangulation measurements. They lie close to the surface but are hard to find as they are often covered with grass. Even harder to find are Surface Bolts such as the Laddow Rocks one. It is amazing that a small bolt has survived all this time.

And sometimes a triangulation point just isn’t one. This is the case of the Hey Edge Pillar which is marked on the map as a Pillar, but does not have the blue triangle on the map. That is because whilst it was built it was never used for triangulation. It was used for levelling, but as I have said that is a totally different set of measurements. Hence it does not qualify as a trig point to Ordnance Survey.

Nowadays with GPS triangulation by hand is no longer required and the Ordnance Survey network of triangulation points is falling in to disuse, apart from a few that is. The Triangulation Pillar at Harland South forms part of the Global Positioning System network, as does the Fundamental Benchmark on Broomhead Moor.  So even though GPS is now the dominant measuring system for position, it still relies on spots on the ground for accuracy.

Triangulation Points

I like collecting things. Triangulation points are a favourite along with benchmarks that can be found along a walk or near to one.

There is something very satisfying about reaching a trig pillar, partly I guess because they invariably involve a walk up hill and a reward of sweeping views, weather permitting. There are 84 pillars within the Peak District National Park boundary and many more triangulation points and thousands more benchmarks.

Some are not shown on maps with the traditional blue triangle, the one at Hey Edge for instance, built but never used for triangulation, but was used for levelling, so does it not qualify for the blue triangle.

Some triangulation points are not even pillars. One of my walks takes in the Hunting Tower on the Chatsworth Estate, the triangulation point being the flagstaff. Another is the centre of the spire of All Saints Church in Bakewell.

With the advent of GPS the triangulation pillar network became largely redundant, but a few still do have a purpose. The pillar at Harland South, levelling bracket number 2998 is part of the Global Positioning Network and as such is protected by Ordnance Survey. A plate informs the visitor that any damage should be reported to the phone number.

Triangulation points always come in a minimum of three so a favoured walk of mine takes in the Hunting Tower at Chatsworth, the pillar at Birchen Edge along with the Three Ships and the pillar at Harland South, passing Hobs House, one of the first ancient monuments to have legal protection in the UK, on the way. Two pillars, one part of the Global Positioning System and one flagstaff on a hunting tower. Not bad for a day out.

Trigpoint Walks 10

SK 2650 7062 The Hunting Tower
SK 2650 7062 The Hunting Tower

I am not a big fan of the country house estate.  The architecture and landscaping is something to be admired, all that human ingenuity, hard work, and skill, but the privilege that is enjoyed by the owners of these huge estates for some dubious acts way back in history is well out of place in my socialist world.

I started my walk from the Chatsworth car park and climbed through the woodland surrounding the house to gain my first trigpoint.  The Hunting Tower is a rather fine trig, possibly one of the best in the country.  The door was open and a lady, I doubt it was the Duchess of Devonshire, was preparing a large table with linen and cutlery. Monty soon found the open doorway and went in the introduce himself and to plant his muddy feet all over the clean tiled floor. I hastily followed to get him out as Monty jumped up and pawed the lady’s clean white apron. No sooner had I entered, only to have Olly follow suit and then all four of us did a sort of dervish dance around the table until the boys left and the lady, in remarkably good humour gently closed the door.

SK 2782 7309 Birchen Edge 310m
SK 2782 7309 Birchen Edge 310m

Relieved at not being incarcerated in The Hunting Tower we headed over to Birchen Edge and our next trig.  Lots of climbing taking place along the edge, young and old all enjoying the sun and the grit stone.  I sat and watched a group pick their way up a route, each man showing lesser or greater skills.  The triangulation pillar is a fine viewpoint and you can see the delineation of the White and Dark Peak. Large plantations of conifer cover the hillsides and no doubt one day will be felled leaving a denuded hill with the grey skeletal remains of the trees, a sight I have never been pleased with.

SK 3008 6815 Harland South 367m
SK 3008 6815 Harland South 367m

Retracing my steps back on to the Chatsworth estate I headed for the final trig of the day, across moorland to a Harland South, which sounds as though it should be a motorway service station.  It was one of the GPS triangulation pillars, used to make sure that the GPS system is behaving. Odd that a technology constructed by pencil and paper should be used to verify a high tech all singing all dancing satellite system.

The route back to the car followed quiet country roads, green lanes and then back down through the estate woodlands to regain the car park. The journey through the woods gave a pleasant end to the day and I have Joseph Paxton to thank for that.