The Global Positioning System is a network of satellites that orbit the Earth and transmit position and time signals to a large number of GPS receivers (devices such as the GPS units people use in their cars, as well as those used on ships and airplanes and by the military).

The receivers, which can be anywhere on land or sea or in the air, pick up the signals and use them to determine their current position. Wherever you are on the planet, the GPS system will work 24/7.

That said, your GPS device needs to be within direct sight of at least three satellites in order to work properly. Therefore, your location might be displayed incorrectly – or not at all – if you are hiking down a deep ravine or driving through a tunnel. The more satellites your GPS can see, the more information it receives to help it calculate your location. Under ideal conditions, you can obtain a good indication of your altitude too; this can be extremely useful for hikers and climbers.

The GPS system was first used by the U.S. military, just like many other technological advances that have now become part of our everyday lives. Once they could calculate positions with such extreme precision, the American armed forces gained considerable advantages over their adversaries and allies alike. In the 1980s GPS was released for civilian use, and was quickly adopted by the shipping industry, among others. Until then, ships had depended on a 300-year-old technology, the sextant, to figure out where they were.

By the early 1990s, GPS technology had advanced to the point where the receiver and mapping data would both fit into a small box. This paved the way for the launch of the personal and portable GPS devices we use now.

The most popular portable GPS units these days are designed either to be used in your vehicle or held in your hand while you are walking around. A lot of automobile GPS devices can also be used as handhelds when you are on foot.

There are several other ways you can get GPS capability, though. Many smart phones have built-in GPS receivers these days, and there are GPS PDAs, GPS walkie-talkies, GPS sport watches and even GPS units for hunting dogs.

You can also buy devices especially made for recreational boaters, runners, cyclists and bikers.

GPS Buying Tips:

• Introduction
• Some Basic Facts
• What is GPS & How Does IT Work?
• The Most Important Features
• Other Features You Might Want