7JG3+H7 Pyhtää, Finland
The Svartvira point is located on the island of Mustaviiri or Svartvira (Swedish name), in the Gulf of Finland, 30 km south of the city of Kotka. It is situated on flat terrain, surrounded by typical Finnish forest. The point on the ground is marked by a small, matchbox-sized hole carved into the rock. The entire island on which the point is located belongs to the National Park "Itäinen Suomenlahti," open to all visitors. The island is part of an archipelago consisting of about one hundred islands and islets, far from the mainland and any inhabited islands. A boat trip from the mainland takes about 1 hour.
The Struve Arc, once known as the "Russian" and later the "Russo-Scandinavian Meridian Arc," is one of UNESCO's World Heritage monuments. The Arc consists of 265 triangulation points, where measurements were conducted from 1816 to 1852 that allowed determining the exact size and shape of the Earth.
The reference points of this triangulation network were marked in various ways on the ground: depressions carved into rocks, iron crosses, stone pyramids, or specially installed obelisks. Often, they were marked with sandstone bricks laid at the bottom of a pit; sometimes it was a granite cube with a cavity filled with lead, placed in a pit with cobblestones.
During the project to include the Struve Arc in the UNESCO list, which lasted 8 years, special search and geodetic works were carried out in each country to locate the original points. All information from all the countries of the Struve Arc was collected, structured, and standardized.
Not all of the original points were found during the special search and geodetic works carried out in recent years with active cooperation of scientists from interested countries, and, moreover, many of them were found to be heavily damaged. Therefore, only the best-preserved points were included in the World Heritage site — a total of 34.
Sources:
http://www.gototrip.com/publications/geodezicheskaya-duga-struve
https://www.maanmittauslaitos.fi/en/about-nls/themes/struve-geodetic-arc/information-tourists
