vastinmeridiaani

Vastinmeridiaani, in geographic terms, refers to the meridian located at 180 degrees longitude, opposite the Prime Meridian. It is the line where longitude is measured as 180° east or 180° west, and in many representations is written simply as 180°. This meridian is central to the concept of a complete east–west division of the globe in the system of geographic coordinates.

The vastinmeridiaani is closely associated with the International Date Line, which generally follows the antimeridian but includes deliberate deviations to accommodate political boundaries and practical considerations for calendar continuity. Because national and regional areas prefer not to be split across different dates, the date line curves away from a strict 180° path at certain points. As a result, the line is not a perfect circle but a jagged boundary in places, while still remaining opposite the Prime Meridian.

Geographically, the vastinmeridiaani mostly traverses ocean, with only a few landmasses intersecting or lying near the line. In navigation, cartography, and geographic information systems, it serves as a reference for longitude values and for calculations that require handling of wrap-around at the 180° seam. In digital mapping, longitudes are commonly stored within a range such as −180° to +180°, making the antimeridian a natural wrap point for data processing and coordinate transformations.

Vastinmeridiaani is a standard term in Finnish geography and cartography, used to describe this fundamental geographic reference without implying any political boundaries.