The meridians are imaginary lines created by the humans. They are measured in longitude, or rather longitudinal degrees. These lines run from north to south, and all of them merge at the North and South poles, while as they get toward the lower latitudes they are further apart from each other. The longitude is measured east and west from the Prime Meridian, also called Greenwich. The Prime Meridian is the longitude with value of 0 degrees, and everything east or west from it has certain longitudinal value between those 0 degrees and 180 degrees. The meridian that is located on the opposite side of the planet from the Prime Meridian is also the International Date Line, running through the Pacific Ocean, and being the ones form where the time starts to be counted.
