The History of Britain's Trig Points: The Concrete Pillars that Mapped a Nation

Have you ever reached the summit of a British peak and encountered a peculiar concrete pillar standing roughly waist-high? These are triangulation stations, more commonly known as "trig points" or simply "trigs," and they tell a fascinating story of how Britain was mapped with remarkable precision in the days before GPS and satellite technology.

The Origins: The Re-triangulation of Britain

In 1935, the Ordnance Survey (OS) embarked on one of the most ambitious mapping projects in British history: the re-triangulation of Great Britain. This mammoth undertaking, known as the OSGB36 (Ordnance Survey Great Britain 1936), would take nearly thirty years to complete and involve the construction of more than 6,500 trig points across the country.

The Design

The iconic concrete pillar design, known as the Hotine Pillar after its creator Martin Hotine, stands approximately 4 feet (1.2 metres) tall. Each pillar was built to a precise specification:

• A solid concrete base, set deep into the ground

• A hollow centre with a brass plate or spider for mounting surveying equipment

• Three sight holes or vanes for taking measurements

• A unique flush bracket with an identification number

How They Worked

The principle behind trig points was beautifully simple yet mathematically complex. Surveyors would set up theodolites (precision measuring instruments) on top of the pillars to measure angles between other visible trig points. Using triangulation, they could then calculate the precise distances and positions between points, gradually building up an accurate map of the entire country.

Strategic Placement

Trig points weren't placed randomly. Their locations were carefully chosen to:

• Provide clear sight-lines to at least two other trig points

• Offer stability for precise measurements

• Create a comprehensive network covering the entire country

• Take advantage of high ground where possible

This is why you'll often find them on hilltops and mountain summits, though many also exist at lower elevations to complete the network.

The Golden Age

The period between 1936 and 1962 marked the golden age of trig points. Teams of surveyors would trek across the country, often in challenging conditions, to take their measurements. The work was painstaking and required immense patience and precision. Each measurement had to be taken multiple times to ensure accuracy.

Modern Times and Preservation

With the advent of GPS and modern surveying techniques, trig points became functionally obsolete by the 1990s. The OS now uses a network of 110 GPS stations called OS Net for modern mapping.

However, these concrete sentinels remain an important part of Britain's heritage:

• Many are now protected as historical monuments

• They serve as popular landmarks for hikers and mountaineers

• Some are maintained by devoted volunteers

• They often mark significant summits or viewpoints

The Current State

Today, of the original 6,500+ trig points:

• Approximately 4,500 remain standing

• Many have fallen into disrepair

• Some have been painted or decorated by locals

• The Ordnance Survey maintains a database of their locations

• The Trig-pointing UK community actively logs and monitors their condition

Legacy and Cultural Impact

Trig points have become more than just surveying tools; they're now integral to British outdoor culture:

• They often feature in hiking challenges and peak-bagging lists

• Many walkers consider reaching a trig point the true summit of a hill

• They're frequently used as navigation teaching aids

• They appear on countless walking photographs and social media posts

📍 FASCINATING TRIG POINT FACTS

• The highest trig point in Britain sits atop Ben Nevis at 1,345 metres

• Some trig points were built using materials carried up mountains by donkeys

• A few coastal trig points are now underwater due to erosion

• The original construction cost of each pillar was approximately £30

• The most isolated trig point lies on the remote island of St Kilda

• One surveyor had to live in a tent for three months to complete measurements in remote areas

• Several trig points have been painted as minions, letterboxes, and other characters by creative locals

Visiting Trig Points Today

If you're interested in visiting trig points:

• Always respect the surrounding environment

• Don't climb or damage the pillars

• Consider joining the Trig-pointing UK community

• Take photos but leave the trig point as you found it

• Use them as navigational practice points

These humble concrete pillars represent a remarkable chapter in British mapping history. While they may no longer serve their original purpose, they stand as monuments to human ingenuity and determination, reminding us of a time when mapping a nation required boots on the ground and clear lines of sight between hilltops.

So next time you reach a trig point, take a moment to appreciate its role in creating the detailed maps we rely on today. These silent sentinels of the hills have more than earned their place in Britain's landscape and heritage.