The Struve Arc is a chain of survey triangulations streching from Hammerfest in Norway to the Black Sea, through 10 countries and over 2,820 km. These are points of a survey, carried out between 1816 and 1855 by the astronomer Friedrich Georg Wilhelm Struve, which represented the first accurate measuring of a long segment of a meridian. This helped to establish the exact size and shape of the planet and marked and important step in the development of earth sciences and topographic mapping. Source: UNESCO
This gallery contains images of the arc in Finland, Sweden and Norway. Here is also a couple of landscape images of the former Finnish Island Suursaari in the Baltic Sea, which nowadays belongs to Russia.