Jumaat, 13 Mac 2009

Latitude and Longitude

The first important question a map-user must answer is: "What part of the Earth's surface is being shown?" In order to answer this question, a map-user must be able to say exactly where a location is on the surface of the Earth. The location of points or areas on the surface of the Earth can be shown by latitude and longitude.

Lines of Latitude and Lines of Longitude

•Lines of latitude circle the Earth in east-west-parallels which are at right angles to the Earth's axis.
•The value of lines of latitude increases in towards North or South from the zero degree line around the middle of the Earth.
•What is another name for that zero degree line of latitude? Lines of latitude increase from the equator at 0 to the North or South pole at 90 degrees.

•Lines of longitude circle the Earth from North Pole to South Pole parallel to the Earth's axis.
• Lines of longitude increase in value, east or west, away from the zero degree line of longitude called the Prime Meridian.
•Because there is no natural vertical 'middle' to the Earth, the Prime Meridian is defined as the North to South circle that passes through the town of Greenwich, England
•(the reason for this is historical: Greenwich was the site of the British Royal Observatory and of the telescope used to make the astronomical observation on which the longitude system was originally based).

•Both latitude and longitude lines represent divisions of a circle and are measured, like circles, in degrees, but also minutes, and seconds.
•There are 60 minutes in a degree, and 60 seconds in a minute.
•Why do minutes and seconds represent divisions of a degree?

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