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 Pillars

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SK 0239 8794 Lantern Pike S 2779 359m

Last year I started to collect all the Ordnance Survey triangulation points in the Peak District National Park boundary. I am about half way through now, although it was supposed to be finished within the year, but the days ran away with me.

There are 94 points if memory serves me correctly. The points are buildings, surface blocks, pins and the king of all tick list features, triangulation pillars.

I try to do a walk that includes 3 points, hence triangulation, its a bit of OCD within me that likes uniformity, it wouldn’t seem right doing four points.

Doing the research is fun, I didn’t know actual buildings could be points, but it makes sense. Bakewell church and the Hunting Tower at Chatsworth are two good examples. High with good lines of sight. I looked a bit weird in the Church with my GPS outstretched moving around one pace at a time, looking at my hand then looking up at the spire, and this was inside too.

Finding a surface block in thick undergrowth is very satisfying as is navigating to a pin. Some I have had to go back to as time has caught up with me before I have found them.

The best feeling is reaching a triangulation pillar. It generally involves an uphill slog, sometimes via a circuitous route, often with the pillar staying out of sight until the last few hundred meters. I think the hard work getting there is part of the joy I feel once I am at the spot. Then there is the view and searching for the, at least, other two that should be able to be seen in the distance.

Some of the pillars are a bright white, some have the lovely mottled concrete surface. Some have been adorned with plaques, some have graffiti. There are some that have been obliterated all together and some that lay forlorn away from their original site. Some hide in hedges, all pristine as the day they were made.

A summers day in a field, sat by a trig pillar that nestles in a hedgerow, eating my sandwiches while birds twitter on and the view looks all sky blue and green grass is one of the happiest ways to spend a few hours.

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Noton Barn SK 2166 6616 S4183 208m