The references for latitude and longitude are quite different. The latitude reference is the equator. This is really define by the polar axis - the line that the earth rotates about each day. This is a reference defined by the physical properties of the earth.
A picture taken at night in a dark area can dramaticly demonstrate the rotation of the earth. If the camera is pointed north, the stars will make trails in circles about the polar axis of the earth.
This photograph was taken at an amateur astromoner convention in west Texas. If you look closely at the original photograph, you can see that even the north star (Polaris) is makes a small circle. It is offset from the rotation axis by a fraction of a degree
The zero of longitude could be anywhere. Today we take it as being through the British Royal Observatory at Greenwich. In the past every major country had its own zero of longitude, usually through an official astronomy observatory. This was because astronomy observations were used to determine latitude and differences of longitude. In 1878 at a conference in Washington DC Greenwich was defined to be the international standard zero of longitude. It was decades before this was commonly adopted though.
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