longitude is an imaginary line running from the north pole to the south pole.The prime meridian,which passes through Greenwich , England ,is longitude 0 .It sets the world standard time and divides the world into the Eastern Heisphere and the Western Hemisphere.From the Prime Meridian at 0 to the west,the range of longitudes is from 0 to 180 West,and from the prime meridian at 0 to the east;the range of longitudes is from 0 to 180 east.