General 2

The circumference of the Great Circle that includes the hypothetical axis “N and S” – the geographical poles is called a Meridian.
Therefore the line joining N and S is a Meridian.
The Meridian Planes intersect at the axis of the earth.
The meridian that passes through Greenwich is called the Prime Meridian or Greenwich Meridian and this divides the earth into two hemispheres:
The hemisphere lying east of the Atlantic that includes Europe, Asia, Africa and Australia, is called the Eastern Hemisphere, and the other half lying west of the Atlantic including North and South America, is called the Western Hemisphere.
To define a location or position on the surface of the earth (except at the poles), we use Geographical coordinates.
As a base and starting point for these coordinates we rely firstly on the Equator, and secondly on the Prime Meridian.
The coordinates are the Geographical Latitude and the Geographical Longitude.