 Mathematics of Cartography  
Great! Interactive Map Site  Mathematics TopicsCoordinate System  
Coordinate systemsNumeric methods of representing locations on the earth's surface. Latitude and Longitude The most commonly used coordinate system today is latitude and longitude angle measures, expressed in degrees, minutes, and seconds.  
Equator and Prime Meridian The Equator and the Prime Meridian are the reference lines used to measure latitude and longitude. The equator which lies halfway between the poles is a natural reference for latitude. A line through Greenwich, England, just outside London, is the Prime Meridian.  
Latitude Parallels that run eastwest. Longitude Meridians that run northsouth.  
Latitude runs from 0° at the equator to 90°N or 90°S at the poles. These lines of latitude, called parallels, run in an eastwest direction. Lines of longitude, called meridians, run in a northsouth direction intersecting at both poles. Longitude runs from 0° at the prime meridian to 180° east or west, halfway around the globe.  
More on Degrees, Minutes, and Seconds On the globe, one degree of latitude equals approximately 70 miles. One minute is just over a mile, and one second is around 100 feet. Length of a degree of longitude varies, from 69 miles at the equator to 0 at the poles. Because meridians converge at the poles, degrees of longitude tend to 0.  
Longitude and Time Since the earth rotates 360 degrees every 24 hours, or 15 degrees every hour, it's divided into 24 time zones 15 degrees of longitude each. When it is noon at Greenwich, it is 10:00 A.M. 30 degrees W., 6:00 A.M. 90 degrees W., and midnight at 180 degrees on the opposite side of the earth.  
Historical Note The planet gave no clear direction on selecting the Prime Meridian, as it did with the equator lying halfway between the poles as the 0 degree of latitude. As late as 1881, there were 14 different prime meridians still being used on topographic survey maps alone. The International Meridian Conference of 1884 adopted the Prime Meridian line passing through the Greenwich Observatory near London, England. Take a trip down the Prime Meridian and explore the countries that lie on it.  

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Copyright December 19962004 Cynthia LaniusURL http://math.rice.edu/~lanius/pres/map/mapcoo.html 