Longitude

Longitude is a way to say where a place is on the Earth. 

It is measured starting from an imaginary north-south line called the Prime Meridian. (A meridian is an imaginary line drawn from the North Pole to the South Pole.) Longitude says how far east or west of the Prime Meridian any place is.

Longitude is measured using degrees, the same way an angle is. The Prime Meridian is 0° (zero degrees), and the farthest away is +180° eastward and -180° westward. 

Latitude, longitude and the prime meridian

http://www.youtube.com/watch?v=YGdw2743vKc&feature=related

The moving picture demonstrates latitude, longitude and the prime meridian.

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Latitude and longitude

Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees (marked with °). The equator has a latitude of 0°, the North pole has a latitude of 90° north (written 90° N or +90°), and the South pole has a latitude of 90° south (written 90° S or −90°). Together, latitude and longitude can be used as a geographic coordinate system to specify any location on the globe.


Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds.

Points with the same longitude lie in lines running from the North Pole to the South Pole. The Prime Meridian, which passes through the Royal Observatory, Greenwich, England, establishes the position of zero degrees longitude. The longitude of other places is measured as an angle east or west from the Prime Meridian.



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