At the beginning of the 19th century, the German-Russian astronomer Wilhelm von Struve decided to make use of triangulation measurements to determine the exact shape and size of Earth. Triangulation measurements mean that the position of a particular point is determined by measuring the distance and angles of the Earth´s surface in triangles. Today we use satellites and Global Positioning System (GPS) instruments to do this.

Struve Geodetic arc consists of 265 triangulation survey stations, each situated at a distance of 30 kilometres from the other, and covering a distance of 2,820 km from Hammerfest in Norway to Izmail on the Black Sea. These triangulation stations marked a great step forward in the research and development of topographical mapping. In July 2005, 34 of the 265 triangulation stations were selected for inclusion as World Heritage Monuments, and are characterised by bored holes, iron crosses, cairns or obelisks.

Struve carried out his triangulation measurements between 1816 and 1855. Through them he was able to substantiate that the latitude meridians were some ten metres shorter in Scandinavia than at the Equator. This was proof that the Earth was not a perfect sphere but oval in shape, and that as the Earth rotated, its mass was drawn towards the Equator and the poles flattened out.

Struve Geodetic arc cuts through ten countries: Norway, Sweden, Finland, Russia, Estonia, Latvia, Lithuania, Belarus, Moldova and the Ukraine. Sweden has seven triangulation stations, four of which are included in the list of World Heritage Monuments. They can be located on the mountains of Tynnyrilaki, Jupukka, Pullinki and Perävaara, situated in the municipalities of Kiruna, Pajala, Övertorneå and Haparanda. Finland boasts 83 triangulation survey stations, six of which are classed as World Heritage Monuments. In Norway, four stations are included in the World Heritage List.

See also:
Struve Geodetic Arc - the National Land Survey of Finland website.
Struve Geodetic Arc - UNESCO.