The Greenwich Meridian, or prime meridian, is the imaginary line that runs through Greenwich, England, and it is designated as 0 degrees longitude. This line is used as a starting point for measuring the lines of east and west longitude, and it helps create the Eastern and Western Hemispheres. It was chosen as the standard in 1884 at an international convention of 25 countries.
The Greenwich Meridian also establishes the International Date Line and the Coordinated Universal Time. There are 24 different times zones in the world, all of which have been measured based on the UTC. The International Date Line is measured at 180 degrees longitude from the Greenwich Meridian.