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Unless your are just using your GPS to find the nearest McDonalds or ATM you will need to learn a little about map coordinates. A GPS coordinate converter will convert different formats of coordinates into the format you want to use or are most comfortable with. GPS devices use signals from the GPS satellites to compute locations or coordinates in the form of latitude and longitude.
Latitude is a measurement in degrees away from the equator towards one of the poles. Longitude is the number of degrees a position is east or west of the prime meridian which passes from pole to pole through the Royal Observatory in Greenwich, United Kingdom.
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Latitude and longitude coordinates can be formatted several different ways. Your GPS can switch between the different formats, but you will be probably most comfortable with one format. Here are the different formats and how they look using the coordinates for the famous Palacio Salvo in Montevideo, Uruguay:
Degrees, Minutes, Seconds: S34° 54' 24", W56° 11; 54" This is the classic method of showing coordinates. There are 60 minutes, indicated by the apostrophe, in a degree and 60 seconds -- quote mark -- in a minute.
Decimal Degrees: -34.906725, -56.198308 Minutes and seconds are converted to decimal places and south latitude and west longitude are given minus signs. This format is easy to type into navigations systems with a numeric keypad.
GPS Coordinates: S34 54.404, W 56 11.898 This format converts just the seconds to decimal places on the minutes. The format is useful when plotting coordinates on a map. Maps of 100,000 or 250,000 to 1 will have tick marks for the minutes on a grid. Having the minutes in decimal form makes it easy to estimate between the minute ticks on a map.
- A side note: One minute of longitude is one nautical mile. For planes and ships measuring speed in knots, this is a handy map reading hint. The fighter pilot flying low level at 480 knots knows that he will cover 8 ticks of longitude every minute.
UTM Coordinates: 21S 573238 6137007 UTM is a grid system used primarily by the military that divides the land mass of the planet into one kilometer squares. Once it is understood, UTM is a very accurate way to pinpoint locations -- and targets! The system is popular in northern Canada where the narrowing longitude lines makes accurately plotting latitudes more difficult.
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Converting GPS Coordinates
GPS navigation devices can use all of the forms of position coordinates, but will work in only one format at a time. It can be a time saver to convert dissimilar coordinates into the same format or a list of nav points into the format you prefer. The solution is one of the numerous online coordinate converters. Many websites that promote outdoor activities will have a page for conversion.
Here is an online converter hat does all formats with one calculation: GPS Coordinate Converter, Maps and Info
Remember to always check the results to make sure they make sense.
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USDA Forest Service: http://www.fs.fed.us/database/gps/datum/index.htm
Charles Sturt University: GPS Coordinate Explanation: http://www.csu.edu.au/australia/latlong/coord.html
Photo credit: pviojo on Flickr, Creative Commons attribution