Most of us never need to use numeric GPS coordinates to take advantage of the many location-based services available to us. We simply enter an address, or click through from an Internet search, or automatically geotagged photos, and our electronic devices do the rest. But dedicated outdoorsmen, geocachers, pilots, sailors, and more often need to use and understand numeric GPS coordinates.

The global GPS system doesn't actually have a coordinate system of its own. It uses "geographic coordinate" systems that existed before GPS, including.

GPS coordinates are usually expressed as latitude and longitude. This system divides the Earth into latitude lines, which indicate how far north or south a location is from the equator, and longitude lines, which indicate how far east or west a location is from the prime meridian.

In this system, the equator is at 0 degrees latitude, with the poles at 90 degrees north and south. The prime meridian is at 0 degrees longitude, and extends from east to west.