Companies such as 24TimeZones.com, Time and Date AS and WorldTimeZone.com publish international time zone maps. These maps show the 24 time zones into which the world is divided, with Greenwich Mean Time and the International Date Line as the major features.
Since 1972, Coordinated Universal Time has been the basis of civil time. It follows International Atomic Time, unlike the Greenwich Mean Time standard that was calibrated to solar mean time beginning in 1847. Greenwich, in London, is the prime meridian or zero longitude point of the world. It divides the western and eastern hemispheres. The International Date Line is located approximately 180 degrees east or west of the prime meridian and marks the divide where the date changes by one day.