About
Somebody had to keep counting.
Between 1935 and 1962, Ordnance Survey built 6,557 concrete pillars across Great Britain and used them to triangulate the country. The modern map was made from these points. Then the work finished, and the archive stopped being maintained.
The data
Where it comes from.
Pillar positions come from Ordnance Survey’s own triangulation archive, published under the Open Government Licence. Hill data comes from the Database of British and Irish Hills, licensed under CC BY 4.0. Both are public, and we cite both.
We deliberately don’t build on OpenStreetMap or Wikipedia. Both carry share-alike terms, and a register that might one day have to be given away is not a register anyone should rely on.
What OS can’t tell you
What’s still there.
The archive is a record of where pillars were. Around 493 have been demolished, buried, or lost to coastal erosion, and stations marked intact may have gone decades ago. Nobody is updating it.
That gap is the whole reason this exists. Every member who confirms a pillar, photographs a broken one, or reports a blocked approach makes the register a little more true than the official one.
The name
Trig. is short for triangulation, which is what all this was for.
The mark is a plain triangle — triangulation is what a trig point is for, and the shape holds even at 16px in a browser tab.