Sari sent me this maxicard which shows one of the many survey triangulation towers.
In Korpilahti, at the top of Oravivuori, lies Oravivuori triangulation tower, one of Finland's six points in the Struve chain. This is a triangulation chain extending from the Black Sea to the Arctic Ocean that was used in the 19th century to establish the shape of the earth. On this spot a triangulation tower has been erected to commemorate the importance of the Oravivuori (or Puolakka) measuring station to the mapping of Finland.
The Struve Geodetic Arc is a chain of survey triangulations stretching from Hammerfest in Norway to the Black Sea, through ten countries and over 2,820 km, which yielded the first accurate measurement of a meridian.
The chain was established and used by the German-born Russian scientist Friedrich Georg Wilhelm von Struve in the years 1816 to 1855 to establish the exact size and shape of the earth. At that time, the chain passed merely through two countries: Union of Sweden-Norway and the Russian Empire. The Arc's first point is located in Tartu Observatory, where Struve conducted much of his research.
In 2005, the chain was inscribed on the World Heritage List as a memorable ensemble of the chain made up of 34 commemorative plaques or built obelisks out of the original 265 main station points which are marked by drilled holes in rock, iron crosses, cairns, others.
Measurement of the triangulation chain comprises 258 main triangles and 265 geodetic vertices. The northernmost point is located near Hammerfest in Norway and the southernmost point near the Black Sea in Ukraine. This inscription is located in ten countries, the most of any UNESCO World Heritage.