Placas Altitud
Plaques from the Spanish Instituto Geográfico y Estadístico to measure the height in relation to the sea level, using alway Alicante because of the small difference between tides.
In 1856 the Instituto Geográfico y Estadístico was created to elaborate a topographic map of Spain, using, among other things these kind of plaques.
The work ended by 1966.
In 1968 there were 2150 signs, of which 428 were in railway stations.
Most of the plaques were placed before 1925 (the inscription reads: Instituto Geográfico y Estadístico), and some after 1925 (the inscription would say: Instituto Geográfico y Catastral).
All the information is from Jordi Olivé's article:
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