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This article explains Latitude and Longitude
 Latitude and Longitudes
Any location on Earth is described by two references; its latitude and its longitude, collectively these form an imaginary grid that covers the globe. This system was developed in the middle ages and can position objects anywhere in the world to within a few meters.
Latitude
The equator is a line of latitude. It divides our planet into the Northern Hemisphere and the Southern Hemisphere. Other lines of latitude run parallel to the equator, either above it (northwards) or below it (southwards). Thus, lines of latitude are also called parallels. They run horizontally around the globe. Parallels measure distance north or south of the equator. This distance is measured in degrees from the centre of the earth.
Each degree of latitude is approximately 69 miles apart; there is a variation due to the fact that the earth is not a perfect sphere but an oblate ellipsoid (slightly egg-shaped). To remember latitude, imagine them as the horizontal rungs of a ladder ("ladder-tude").
Degrees latitude are numbered from 0° to 90° north and south. Zero degrees is the equator. 90° north is the North Pole and 90° south is the South Pole.
 Longitude
Another set of imaginary lines helps us measure distance east and west of Greenwich in London. These are lines of longitude. Lines of longitude (also called meridians) converge at the poles and are widest at the equator (about 69 miles).
Longitude lines are measured in degrees East or West of Greenwich, London. The Meridian that runs through Greenwich is called the prime meridian and is 0o longitude.
Angles of Longitude cannot exceed 180 o E or W.
Latitude and Longitude
To precisely locate points on the earth's surface, degrees longitude and latitude have been divided into minutes (') and hundredths of minutes. There are 60 minutes in each degree.
Example Position References
Positions are always quoted in the following format (always Latitude first):
Greenwich = 51o 29' 00"N 000o 00' 00"W
Charts
One nautical mile is one minute of meridian latitude.
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