Pituuslinjat

pituuslinjat are the lines of latitude on a geographic map or globe that represent circles of constant distance from the equator. These lines are measured in degrees, minutes, and seconds, with the equator at 0°, the Tropic of Cancer at approximately 23.5° north, the Tropic of Capricorn at approximately 23.5° south, the Arctic Circle at about 66.5° north, and the Antarctic Circle at about 66.5° south. Unlike meridians, which run north to south, pituuslinjat run east to west and are centered on the Earth's rotational axis.

In cartographic practice, pituuslinjat are used to designate regions, determine climate zones, and provide reference points for navigation. They appear in most world atlases, nautical charts, and GPS systems, often with brief labels indicating the latitude. The term "pituuslinjat" is borrowed directly from Finnish, wherein "pituus" means "latitude" and "linja" means "line". In other languages the concept is known as parallels, parallels of latitude, or simply latitudes.

The calculation of a point's latitude involves measuring the angle between the equatorial plane and a line extending from the Earth's center to the point on the surface. Modern techniques employ satellite geodesy, where precise measurements are taken from GPS or other global navigation satellite systems. Historically, celestial observations were employed, using the zenith distance of stars to determine latitude. Pituuslinjat remain fundamental to geographic information systems, helping stakeholders understand spatial relationships within a global context.