If you’ve done much walking in Britain – especially on high ground – you’ve almost certainly come across a trig point or two.
About four feet (1.2m) high and made of rather unflattering concrete or (more rarely) cemented stone, these little pillars dot the land like freckles. And you may well have wondered what they’re doing there.
What was the first trig point?
Officially known as triangulation stations or trigonometrical points, the four-sided trig pillars began life in Britain in 1935 on the drawing board of Brigadier Martin Hotine of the Ordnance Survey (OS). The first one was erected by the OS the following year near Cold Ashby, Northamptonshire. It would eventually be joined by over 6,500 more, covering the whole of Great Britain.
What's the purpose of trig points?
The pillars are not necessarily found on summits as is often supposed, but are located in positions where they have uninterrupted sight-lines to at least two other trig points. By taking measurements with theodolites set up on the brass plates (‘spiders’) that top the pillars, cartographers were able to build up a network of triangles that could be used as a basis for exceptionally accurate map-making.
What is trig-bagging?
Today, the popular pastime of trig-bagging involves chalking up visits to these trig points in much the same way a fan of mountains might bag Munros. Although there’s little agreement among aficionados about which are the country’s best trig points, there are two that stand out from the rest: the highest (1344m) looks out from the summit of Ben Nevis, while the lowest sits at 53cm below sea level near Little Ouse on the Norfolk/Cambridgeshire border. It's thought that Rob Woodall, from Peterborough, bagged all of the trig points in the UK in 2015.
- Why some places are more 'thankful' than others. Discover the shameful secret behind the villages with no war memorial
- Why is the poppy a symbol of remembrance?
- Where's the longest pier in the world? Clue, it's in Britain and it's over a mile long...
Are trig points only found in the UK?
Britain is by no means alone in having used this method of map-making – you’ll find trig points in countries all over the world, from Austria, Australia and Canada to Ireland, Uruguay and the United States. They come in all shapes and sizes too, such as Hong Kong’s small funnel-like affairs and Finland’s huge wooden pylons. But they all serve (or served) the same purpose – to help cartographers create more accurate representations of the world we inhabit.
Are trig points still used today?
In recent years, the OS has adopted more modern methods of charting the landscape, using aerial photography, drones and satellite data. As a result, the stock of the nation’s trig points has begun to decline slowly, as those that are crumbling away are not repaired or replaced.
- How to read map symbols
- Keep your maps dry: Best waterproof map cases reviewed
- How to measure distance
But even today Britain’s trig pillars serve a very useful purpose. Each one is shown on OS maps by a blue triangle with a dot in the centre. So if you’re out and about with a map and have no GPS to guide you, a trig point can act as a trustworthy landmark to help you find your way.
