The British Cartographic Society (BCS) was formed in 1963, and since then map-making has undergone a revolution, from land survey using theodolites to digital survey using satellites. But the infrastructure for the old ways still exists and the most recent issue of Maplines, the BCS membership magazine, calls for Ordnance Survey benchmarks to be given greater protection.
Cut into stone at the base of a building, church, or bridge, benchmarks consist of a horizontal bar above an upward-facing arrow. The height above sea level of every benchmark is known, so surveyors can use this to find the elevation of any other point above or below that of the benchmark using a theodolite and a measuring rod. ‘Benchmark’ has thus entered the language to mean the standard to which something else is compared.
About half a million of these ‘lower order’ benchmarks are in existence today (another 250,000 have been lost through wartime damage, wear and tear, and building demolition or refurbishment) so protecting them all is a forlorn hope, but there are fewer than 200 fundamental benchmarks (FBMs) that could be protected. Mostly constructed in the first half of the 20th century, FBMs comprise a foot-high stone pillar, anchored to the bedrock, with a nameplate declaring it to be an ‘Ordnance Survey BM’; about half of them are surrounded by railings.
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