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.