Why Do Mapmakers Draw Lines of Latitude?
Lines of latitude are drawn from east to west on maps and globes. Together with lines of longitude--which are drawn from north to south--they form a grid which allows you to specify the location of any point on the Earth's surface. According the U.S. Geological Survey's National Atlas of the United States, this can be done to within inches. For example, the Statue of Liberty stands at latitude 40.68913 degrees north and longitude 74.0446 degrees west.
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History
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The system of latitude and longitude was devised by the Greek mathematician and astronomer, Ptolemy, who lived in the Egyptian city of Alexandria during the second century. His seven-volume work "Geographica" gives coordinates for 8,000 different places, according to the Center for Spatially Integrated Social Science. In the days of tall ships, sailors used a device called a quadrant to establish their latitude by working out the angle between the horizon and the North or South Poles.
Angle Not Distance
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Latitude is a measure of angle rather than distance. Imagine a cross-section of the Earth; a flat circle like a big pie. Each line of latitude marks the point on the edge of the pie where a knife would cut through to the center to take a slice. There are 90 degrees of latitude in the northern half of the globe and 90 degrees of latitude in the southern half. These halves of the globe are often called hemispheres.
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Equator
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The Equator is an imaginary line which circles the Earth at an equal distance from both the North and South Poles. It is positioned at latitude zero degrees, and is the starting point from which all other latitudes are measured. All lines of latitude run parallel to the Equator and are sometimes called "parallels" for this reason. Lines of latitude are evenly spaced at approximately 69 miles apart.
Degrees or Decimals
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Latitude and longitude are measured in degrees, minutes and seconds, in the same way as any other angle, but they can also be shown as decimals. If a latitude is preceded by a minus sign, this shows it is in the southern hemisphere. In the same way, a minus sign in front of a longitude reference is used instead of the word "west."
Special Latitudes
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The "low latitudes" are warm areas of the Earth, between the 30th parallels to north and south of the Equator. The "high latitudes" are cold areas, to the north and south of the two 60th parallels. Four other well-known lines of latitude are the Tropic of Cancer, the Tropic of Capricorn, the Arctic Circle and the Antarctic Circle. These lines give us a handy way to describe differences in climate. So, lines of latitude help us to find exact locations on the Earth and also to work out what the weather will be like when we get there.
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References
- Photo Credit Globe and Hand image by Towards Ithaca from Fotolia.com
