GPS (Global Positioning System) is designed to accurately pinpoint a location on earth. GPS capabilities are finding their way into a wide variety of consumer, commercial and military devices. The most popular consumer devices are those designed for car navigation, and these devices can be a great help for many people.

These card-deck sized automotive navigation GPS units come pre-loaded with maps of the United States (and sometimes other areas as well) and will display on a small touch screen your current location on an appropriate map. If you’re planning a trip, you only need to enter your destination to have the device plot a route for you from your current location. Once you’re on your, trip you’ll get voice prompts for turns. Less expensive GPS units such as the TomTom ONE 125 (www.tomtom.com, $129) have a three-inch screen and voice prompts such as "turn left in 300 feet." More expensive units such as the Magellan RoadMate 1412 (www.magellangps.com $249) will have a four inch screen and voice prompts speaking the name of the street and the number of feet before the turn, such as "turn right onto Wildwood Road in 200 feet."

Additional functions may be found on the even more expensive units. For example, the Garmin nuvi 880 (www.garmin.com, $799.99) can use voice activation for entering your commands and can also play MP3 music or audio books through its own speakers or, using the built-in FM transmitter, through your car radio/audio system. In addition, using its built-in Bluetooth, the unit can be used for hands-free cell phone calls. A built-in FM receiver tunes to MSN Direct (where available) for the latest in area weather, traffic reports and entertainment news. An anti-theft password protected system disables the unit if removed from car. And a "Where am I?" feature displays nearby hospitals, police stations and gas stations.

With the three major GPS manufacturers providing more than 60 different models of navigational devices, all sporting tons of features, choosing the unit that’s right for you can be a bewildering task. As you can see, the more you pay for most GPS devices, the more features and functionality you get. We’d advise you to use one of the Internet product comparison sites such as www.buzillions.com to see what users have to say about any specific unit you might be interested in.

As an option to a dedicated unit for car navigation, you can add an external GPS receiver such as the Earthmate GPS BT-20 Receiver (www.delorme.com, $99.95) to your laptop, mobile or ultra-mobile computer. Included is Street Atlas USA 2009 plus, a full-featured trip planning and mapping software. The combination of this receiver and your computer provides a much larger screen display while preserving much of the features and functionality of the dedicated units.

Handheld GPS units are very useful for sportsmen (and women), hikers and bikers, boaters, outdoor workers and the like. A handheld unit such as Earthmate GPS PN-40 (www.delorme.com, $499.95) can plot routes by using its 8GB internal memory and can also easily hold and display topographical maps, satellite and ariel photos of the regions you’ll be traveling through.

You’ll also find cell phones and digital cameras with GPS capabilities that indicate where you’re calling from or where your photos were taken. For gaming, there’s a GPS scavenger hunt. And these are only a few of the many uses and applications of GPS devices.

GPS 101: GPS is a system of 24 or more satellites circling the earth in six orbital planes. The time signals broadcast by the satellites are compared by your GPS receiver, and the very tiny time difference in arrival of the signal due to the different distance of the satellite from your receiver is calculated to determine latitude, longitude and height above sea level of the location of your receiver. The receiver needs signals from at least four satellites to get a 3-D fix (latitude, longitude and height above sea level). For three signals, you get a 2D fix (latitude and longitude). Any GPS receiver must "see" the satellites to receive a strong enough signal to use, but placing the receiver on the car’s dashboard works fine, since the signals travel through the windshield glass. Go through a tunnel, however, and you’ll lose the signal temporarily. Sometimes signals will be weak enough to be lost in heavily wooded areas due to the trees or in urban areas because of tall buildings.

The satellites are owned and operated by the Department of Defense, primarily to aid in military operations. Initially, two types of GPS signals with different accuracies were available from the satellites: one for civilian use and the other for military and governmental agency use. More recently, however, the governmental restriction on accuracy has been lifted, and full accuracy is available for all users. Positional accuracy for the signals depends on several factors but is about 3 to 12 meters for most consumer uses. For specialized uses such as land surveying, a second high sensitivity receiver is added, and centimeter accuracy is possible.