Longitude is a measurement of location east or west of the prime meridian at Greenwich, the specially designated imaginary north-south line that passes through both geographic poles and Greenwich, London.
Unlike the parallels of latitude which are circles, the meridians of longitude are semi-circles that converge at the poles.
If opposite meridians are taken together, they complete a circle, but, they are valued separately as two meridians.
The meridians intersect the equator at right angles.
Unlike the parallels of latitude, they are all equal in length.
For convenience of numbering, the meridian of longitude passing through the Greenwich observatory (near London) has been adopted as the Prime Meridian by an international agreement and has been given the value of 0°.
The longitude of a place is its angular distance east or west of the Prime Meridian. It is also measured in degrees.
The longitudes vary from 0° to 180° eastward and westward of the Prime Meridian.
The part of the earth east of the Prime Meridian is called the eastern hemisphere and in its west referred to as the western hemisphere
The vertical lines running north-south, join the two poles. They are called the meridians of longitude. They are spaced farthest apart at the equator and converge at a point at each pole.
Measured also in degrees, minutes, and seconds, longitude is the amount of arc created by drawing first a line from Earth’s centre to the intersection of the Equator and the prime meridian and then another line from Earth’s centre to any point elsewhere on the Equator.
Longitude is measured 180° both east and west of the prime meridian.
As aids to locate longitudinal positions on a globe or map, meridians are plotted and drawn from pole to pole where they meet.
The distance per degree of longitude at the Equator is about 111.32 km (69.18 miles) and at the poles, 0.
