Humanities › Geography Global Positioning System Eight Things You Need to Know About GPS Share Flipboard Email Print enot-poloskun/E+/Getty Images Geography Maps Basics Physical Geography Political Geography Population Country Information Key Figures & Milestones Urban Geography By Matt Rosenberg Geography Expert M.A., Geography, California State University - Northridge B.A., Geography, University of California - Davis Matt Rosenberg is an award-winning geographer and the author of "The Handy Geography Answer Book" and "The Geography Bee Complete Preparation Handbook." our editorial process Matt Rosenberg Updated April 02, 2017 Global Positioning System (GPS) devices can be found everywhere - they're used in cars, boats, airplanes, and even in cellular phones. Handheld GPS receivers are carried by hikers, surveyors, map makers, and others who need to know where they are. Here are the eight most important things you need to know about the GPS. Important Facts About the Global Positioning System The Global Positioning System is composed of 31 satellites 20,200 km (12,500 miles or 10,900 nautical miles) above the earth. The satellites are spaced in orbit so that at any time a minimum of six satellites will be in view to users anywhere in the world. The satellites continuously broadcast position and time data to users throughout the world.Using a portable or handheld receiver unit that receives data from the closest satellites, the GPS unit triangulates the data to determine the unit's exact location (typically in latitude and longitude), elevation, speed, and time. This information is available around-the-clock anywhere in the world and is not dependent on weather.Selective Availability, which made the public Global Positioning System less accurate than the military GPS, was turned off on May 1, 2000. Thus, the GPS unit you can buy over the counter at many retailers is as accurate as those used by the military today.Many over-the-counter handheld Global Positioning System units contain base maps of a region of the earth but most can be hooked up to a computer to download additional data for specific locales.GPS was developed in the 1970s by the U.S. Department of Defense so that military units can always know their exact location and the location of other units. The Global Positioning System (GPS) helped the United States win the war in the Persian Gulf in 1991. During Operation Desert Storm, military vehicles relied on the system to navigate across the barren desert at night. Global Positioning System is free to the world, developed and paid for by U.S. taxpayers through the U.S. Department of Defense.Nonetheless, the U.S. military maintains the capability to prevent enemy use of GPS.In 1997, U.S. Secretary of Transportation Federico Pena stated, "Most people don't know what GPS is. Five years from now, Americans won't know how we lived without it." Today, Global Positioning System in included as part of in-vehicle navigation systems and cellular phones. It's taken a few more than five years but I know the rate of Global Positioning System use will continue to explode.