Tom Scott Explains the Curious Concrete Pillars Found on Many Hilltops in Great Britain

In the latest episode of Things You May Not Know, host Tom Scott (previously) explains a curiosity found in Great Britain–some 6,000 concrete pillars that dot the hilltops of the country. As Scott explains, the pillars are triangulation stations built by Great Britain’s national mapping agency, the Ordnance Survey, between 1936 and 1962. The stations were part of the retriangulation of Great Britain, a project to produce a highly accurate map of the country. Each station, or “trig point,” is located within sight of two others. Thus, simple trigonometry can be used to determine distances between trig points with a high degree of accuracy, and an accurate map can be (and was) created from this information. The Ordnance Survey still keeps a list of trig points for intrepid map fiends and hikers.

photo by Velella