How To Read GPS Coordinates

Some Global Positioning System, or GPS, receivers are now programmed with maps so that the receiver directs you to your exact destination. This is true of the navigation systems manufactured for vehicles. Some of the more technical and precise GPS models give coordinates that must be read and interpreted using a map. 

1. Understand that GPS coordinates are given using longitude and latitude. Longitudinal lines, or meridians, are vertical and denote positions on the Earth from east to west. Lines of longitude are named by degrees depending on how far they are from the Prime Meridian, which is 0 degrees. Lines of latitude are horizontal and denote positions on the Earth from north to south. They are also named by degrees depending on how far they are from the Equator, which is 0 degrees.


2. Understand that most coordinates do not fall at the exact intersection of lines of longitude and latitude. The distance from the closest line is measured in minutes and seconds. There are 69 miles between lines of latitude. A minute is equal to 6,072 feet and a second is equal to 101 feet. For example, if your desired location is 65 degrees 3 minutes 2 seconds north, it is located 18,418 feet north of the 65th line of latitude. There are 42 miles between lines of longitude. A longitudinal minute is 3,696 feet and a second is 61.5 feet.


3. Find your GPS location now that you understand the imaginary lines that map the Earth.


4. Purchase a detailed map of the area in question. Lines of latitude and longitude must be clearly marked. Look for a map compiled using local survey datum. Global survey maps are less accurate.


5. Input the pertinent information into your GPS device following the manufacturer's instructions for that particular model.


6. Plot the coordinates on the map one at a time once the GPS gives the coorindates in their longitudinal and latitudinal form. Find the first coordinate and mark it with a dot. Find the next coordinate and mark it with a dot. Draw a straight line in a north/south direction from the latitudinal point. Draw a straight line in an east/west direction from the longitudinal point. Where those two lines intersect is your desired location.


7. Purchase a Geographic Information System, or GIS program, if you wish the avoid the technical part of using a GPS. These are computer programs that can plot your coordinates on the map for you. This eliminates the need to read and plot the coordinates yourself.