You might find the retriangulation of Britain in the 1930s and 40s interesting [1]. A network of ~6,500 triangulation pillars (trig points) were built across th

You might find the retriangulation of Britain in the 1930s and 40s interesting [1]. A network of ~6,500 triangulation pillars (trig points) were built across the country, each of which were in line of sight of at least two other pillars. The pillars each have a mounting point for a theodolite, to allow their position to be calculated from the relative angle and elevation of other visible trig points. They are often on the top of hills or mountains and so have a warm place in my heart from signifying the high-point of many a hike. [1] https://en.wikipedia.org/wiki/Retriangulation_of_Great_Britain https://en.wikipedia.org/wiki/Retriangulation_of_Great_Brita...