Lines of longitudes are the vertical parallel lines that run from the north pole to the south pole. these are all of equal lengths. Their total number is 360 and are also called Meridians.
The zero-degree longitude is called the Prime Meridian which passes through Greenwich near London in the United Kingdom. From the Prime Meridian, we count 180 degrees towards the east and 180 degrees towards the west. Longitudes towards the east of the Prime Meridian are called the East Longitudes (E) and longitudes towards the west of the Prime Meridian are called the West Longitudes (W).
The prime meridian being the zero-degree longitude, divides the earth into two equal halves called the hemispheres, the western hemisphere and the eastern hemisphere.
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