In the United Kingdom, trigpointing is a recreational activity similar to benchmarking. Searching for trig points is more popular than hunting benchmarks in the UK, but there is a considerable overlap in participation. "Trig points" is the common name for "triangulation pillars". These are concrete pillars, about 4 feet tall, which were used by the Ordnance Survey in order to determine the exact shape of the country in a project known as the retriangulation of Great Britain, which was carried out from 1936 to 1962. 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 setting a theodolite on the top of the pillar, accurate bearings to nearby trig points could be taken. This process is called triangulation.