How do latitudes and longitudes be identified?

Answer 1

They are measured relative to 2 "great circles" around the earth, each identified as 0 degrees. The first is the equator, which is equidistant from the north and south poles. The second is a circle that goes through Greenwich, England and the 2 poles (also known as the prime meridian). Greenwich was chosen because it was the location of the Royal Observatory of the British Empire. The British Navy, as a great power of the world, desired to have the best navigation system possible - their astronomers were helping to devise a solution to this problem, hence defined the longitude system relative to their most desirable location).

If a line is drawn from the center of the earth to a point on the earth's surface, the angle that line makes with the plane defined by the 0 degree latitude (the equator), is the latitude. And the angle of that line with the plane defined by the 0 degree longitude (the one through Greenwich), is the longitude. Also latitudes must define whether the angle goes north or south of the equator, and longitudes must define whether the angle goes east or west of the prime meridian.