The triangulation pillar on Farley Mount
Most triangulation pillars are situated on top of hills, however the summit of Farley Mound is occupied by a pyramidal monument, so this one has to stand to one side. This means that it doesn't have an uninterupted 360 degree view as the Iron Age mound that the monument is on obscures the view to the south-west.
Trigpoints are the common name for these "triangulation pillars". These concrete pillars, are about 4' tall, and were used by the Ordnance Survey in order to determine the exact shape of the country. They are generally located on the highest bit of ground in the area, so that there is a direct line of sight from one to the next. By sitting a theodolite (an accurate protractor built into a telescope) on the top of the pillar, accurate angles between pairs of nearby trigpoints could be measured. This process is called "triangulation".
A major project to map out the shape of Great Britain began in 1936. The network of triangulation pillars, with accurately known positions, led to the excellent OS maps. The coordinate system used on these maps is known as the "National Grid", and it is essential that you are familiar with this system if you are to get the most of OS maps.
The triangulation pillar on Farley Mount
Most triangulation pillars are situated on top of hills, however the summit of Farley Mound is occupied by a pyramidal monument, so this one has to stand to one side. This means that it doesn't have an uninterupted 360 degree view as the Iron Age mound that the monument is on obscures the view to the south-west.
Trigpoints are the common name for these "triangulation pillars". These concrete pillars, are about 4' tall, and were used by the Ordnance Survey in order to determine the exact shape of the country. They are generally located on the highest bit of ground in the area, so that there is a direct line of sight from one to the next. By sitting a theodolite (an accurate protractor built into a telescope) on the top of the pillar, accurate angles between pairs of nearby trigpoints could be measured. This process is called "triangulation".
A major project to map out the shape of Great Britain began in 1936. The network of triangulation pillars, with accurately known positions, led to the excellent OS maps. The coordinate system used on these maps is known as the "National Grid", and it is essential that you are familiar with this system if you are to get the most of OS maps.