On the trig-point trail

Trig point on Shining Tor

Bryn Euryn is a limestone outcrop, not much more than 400 feet in height, that lies above the seaside settlement of Rhos-on-Sea on the North Wales coast. Its summit was once occupied by a hill fort which was supposedly a stronghold of Cynlas Goch, a Welsh king who held sway over these parts in the early sixth century. For me, spending many happy holidays on this coastline, the hill held an allure that appealed to the imagination of a small boy. However, it wasn’t the Dark Age fortress that left me spellbound, it was something else that stood on its summit.

For generations, Bryn Euryn had been a popular outing with my father’s side of the family who holidayed in Colwyn Bay, this tradition being continued during my own childhood, so that climbing the hill could almost be considered a rite of passage. When I was old enough to clamber to the top with my dad, I was confronted with a concrete pillar standing around 4 feet tall, which marked its summit. I can still remember the exhilarating feeling when my father held me aloft and sat me down on top of the column so I could marvel at the view. It was my first ever encounter with a trig point.

If you’re the outdoors type and you enjoy roaming the open spaces of the British mainland like I do, you’ll be familiar with these edifices that adorn prominent elevations around the country. As I grew up and scaled ever higher hills, these pillars generally marked the apogee of a walk, and the arrival at the summit would be accompanied by the same ritual of standing on its top, just large enough to take one person. Having one’s photograph taken was (and still is) all part of the proceedings. All the major (and minor) peaks I climbed had them: Bleaklow Hill, Kinder Scout, Snowdon and Ben Nevis. In that respect, these trig points symbolised the culmination of a long and arduous hike. 

There are over 6000 of these pillars in England, Wales and Scotland. Built in the 1930s and constructed in concrete, they are best described as truncated square pyramids which taper towards the top. On the top is a brass mounting designed for holding surveying equipment. They are commonly known as trig points, sometimes just ‘trigs’, but they are more correctly defined as ‘triangulation stations’. This network of stations was used, as part of a massive ‘retriangulation’ scheme, to measure the country more precisely and so render more accurate mapping for the Ordnance Survey of Great Britain (OS).

As a method of calculating distances, triangulation has been known about since ancient times. It is founded on the mathematical principle that the exact position of point C on a triangle can be calculated if the distance from A to B (the baseline) on the same triangle is known and the angle in relation to C can be determined from each end of the baseline. The branch of mathematics which studies such relationships between the lengths and angles of a triangle is known as trigonometry.

Triangulation was used in the ancient Greek, Arab and Chinese cultures to measure heights, slopes and angles and was even used for basic mapping. It wasn’t until the late eighteenth century however, that triangulation came into use on a large scale for mapping purposes. It was an age of scientific discoveries and, against the background of this technical progress, rulers of the day were starting to demand that the true extent of their realms be ascertained. 

Under the patronage of the King Louis XIV of France, Giovanni Domenico Cassini - an Italian surveyor known for his work on waterworks and fortifications - was commissioned in 1669 to produce more detailed maps of France, which would give a much more accurate portrayal of features such as mountains, rivers, cities, roads, political boundaries and other man-made elements. In the first instance, astronomical data was applied to find out the latitude and longitude of any given location and, in combination with triangulation methods, calculations were used to establish the meridian line north and south of Paris. Cassini died in 1712 and was succeeded as general surveyor by his son, Jacques, who was later assisted by one of his own offspring, Cesar Francois. By 1733, fairly accurate charts of France had been plotted and triangulation techniques (using smaller triangles) were then deployed to fill in the details. By 1740 France had been comprehensively surveyed using a network of 400 triangles. Never before had a country been so accurately mapped.

Over time methods of triangulation improved and ever more sophisticated surveying equipment was developed. As the United States expanded westwards, larger and more inhospitable expanses of land needed mapping. This was no less true for colonial powers as they began to explore the hinterlands of their newly acquired possessions. 

Whilst few people would fail in naming the world’s highest peak, the vast majority would probably be oblivious to the fact that the mountain was named after the greatest practitioner of triangulation of his day. George Everest was responsible for completing the Great Arc of the Meridian, which measured the Indian sub-continent from top to toe over a period of 50 years. With instrumentation weighing half a ton, the progress of his team of surveyors was often hampered by hill and jungle, flood and fever, and tigers and scorpions, yet the 1600-mile survey was more or less inch-perfect and resulted in the first accurate measurements of the Himalayas.

As already alluded to, cartography was an occupation that was reserved almost exclusively for the military and it is no coincidence that Britain’s mapping agency is still known as the Ordnance Survey. (George Everest, for example, was a colonel and up until 1974, the post of general director of the OS was always held by a military commander). Things were no different in other countries. 

In Japan, triangulation even became a matter of prestige for its army. By 1900, apart from its very highest mountains, triangulation of the country was all but complete. Only the Tatayame mountain chain had eluded the efforts of its army surveyors. No one had yet scaled the range’s highest peak, Tsurugidake and it was a prime objective of the country’s mappers to put a triangulation station on its summit so that the remote mountain terrain could be accurately charted. It was at a time when mountaineering had emerged as a sport in Japan, and this original goal was soon eclipsed by an even more important objective: who would be the first to scale this hitherto unconquered peak? In 1904, Shibasaki Yoshitaro, the surveyor in charge of mapping the Tsurugi area, was given strict orders by the Imperial Army to make the first ascent before the amateurs of the Japan Alpine Club could do so. Under this pressure and operating with limited financial resources and inadequate mountaineering gear, Shibasaki and his 6 assistants set off to climb Tsurugidake, often having to resist the deep superstitions of the locals. With supreme effort - often having to risk hardship, and not least life and limb on the way - they finally reached the summit on 13 July 1907 and subsequently set up a triangulation station that helped fill in the final pieces of the mapping jigsaw. There was a final twist however: ancient relics from the Middle Ages, namely a rusty iron sword and a sceptre made of tin were found on its summit, so it turned out that an unknown monk had made the undocumented ascent several hundred years before. The story was later made into a novel in 1977 and subsequently into an award-winning film in 2009: Tsurugidake - Ten no Ki, or ‘Chronicle of Stones’. Anyone who is unfamiliar with the beauty of the Japanese mountain landscape should watch this stunning film and it has a great story-line too.

But, I’m getting carried away. This blog was supposed to be about the triangulation pillars like the one at the top Bryn Euyrn which kindled in me a fascination for this omnipresent feature of the British landscape, so perhaps a little more background is required.
 

The network of pillars that cover Britain from the Shetlands to the Scilly Isles was conceived as part of a retriangulation plan in the 1930s. One outcome of an increasingly industrialised and urbanised society was the emergence of town and country planning as an applied discipline. With organised planning came a need for more accurate mapping. The original triangulation of Britain had started in 1784 and continued until 1803, but this had been largely piecemeal and local in character with major deviations between different parts of the country. Retriangulation was part of a master plan to survey the country even more faithfully. 100 locations were identified for the primary stations, partly based on the site of the original triangulation in the 19th century, located about 30 miles apart, where pillars - within view of each other - would be erected. Later, secondary triangles would to be inserted into the primary network, this time each side of the triangle being 5 or so miles long.

Primary pillars were placed almost exclusively on high tops in remote areas, often necessitating the use of packhorses and brute manpower for carrying construction materials uphill. The base needed 3 feet of foundations, otherwise the pillar might topple over on unstable ground, so it is a testament to the integrity of the builders that the overwhelming majority of these pillars stand firm to this day. (Of the 6,500 that were built around 5,500 are still standing.) The war intervened to put a temporary halt to the primary triangulation, but after 1945, secondary and tertiary triangulation - which created an even finer mesh of triangles - was completed and observations concluded in 1952. The results of the retriangulation were used to create the national grid which became the basis of the Ordnance Survey's new maps. This generated a co-ordinate system which is still used today and allows plotting of the entire country with a relative accuracy of just less than 20 metres from north to south.

In the 1990s, with the advance of satellite mapping using GPS technology, it was decided to ‘retire’ the vast majority of triangulation pillars from service. (Some pillars were kept on and incorporated into the GPS network, having signals in their base to keep the satellite system working.) This decision meant that the OS would relinquish responsibility for their upkeep. However, even though they had only been in existence for a relatively short time span (60 years at the most), the trig point had become part and parcel of the British landscape and there was a considerable backlash about this wanton abandonment by the UK's national mapping agency. Questions were even asked in parliament and eventually the OS came up with the idea of a trig point adoption scheme. This meant that private individuals (or clubs) could apply to adopt their own pillar and maintain it on a regular basis, for example, with a fresh coat of white paint. Of course, trig points on popular high-points were quickly snapped up, but those hidden away in hedgerows and on flat, featureless land simply became neglected.

In 2005 I found myself at the top of The Calf, the highest point on the Howgill Fells, a distinctive range of hills that lies between the Lake District and the Yorkshire Dales. From its pristine white triangulation pillar on the summit (626 metres), the extensive panorama takes in the Lakeland skyline and the Yorkshire Three Peaks. My visit to this memorable trig point location prompted me to investigate the subject more closely on internet and I stumbled across trigpointing.uk, the definitive site for trig points and ‘trig-bagging’. The site lists every single triangulation pillar in Great Britain and it’s possible to log visits to individual locations. In fact, trigpointing has become quite a sport and the site has over 2500 registered users, including myself. In the time that has elapsed since my ascent of The Calf, I've managed to bag over 60 pillars – that’s six a year: no mean achievement when you consider I don’t even live in the country. And even though I hold a respectable 400^th position on the all-time rankings, I’m small fry when you realise that someone has actually copped them all!

As it happens, I’m quite happy to keep my trig-bagging exploits to manageable proportions. Many trig points, like the one in the low-lying field 500 yards from where my father lives, are situated in unexceptional locations and only exist because they occupy the highest point in what would otherwise be an unremarkable landscape. Mostly however, these iconic structures stand on isolated tops which afford outstanding views (after all, that’s what they were originally built for), so they invariably provide rewarding destinations for an outdoor excursion. Just like my outing to the top of Bryn Euryn over 50 years ago.