GPS is used for land, sea, and airborne navigation as well as surveying, geophysical exploration, mapping and geodesy, vehicle location systems, and any other applications that may need location information.

The most common use for GPS is navigation. In-car navigation systems use GPS to guide you around the city or through unfamiliar territory. It can suggest the best route from point A to point B, giving you turn-by-turn directions. Some can detect where you've deviated from the suggested course and recalculate another route to bring you to your destination. There are versions specifically designed for maritime as well as airborne use. GPS has helped ships navigate around icebergs and other vessels, ensuring passengers and cargo a safe trip to their destinations.

Handheld GPS receivers work similarly, but are usually designed for recreational activities such as hiking, fishing, hunting, mountain biking, just to name a few. Although hand-help navigation products like Garmin and TomTom are now very popular.

GPS has been an essential part of expeditions through Amazon rain forests to exploring the frigid Arctic. It has helped plot safe routes and mark danger zones for the safety of other explorers who venture into the same area. [Editor's note: I, myself have used them on my own archaeological expeditions in Costa Rica and Peru!]

Another use for GPS is tracking a person, vehicle or object. This does require hardware and software specifically designed for that purpose. GPS tracking can be broken down further into three categories - Data Loggers, Data Pushers and Data Pullers.

A GPS Data Logger records the position of the device at intervals that can be downloaded to a computer for analysis. This can be useful for monitoring numerous things such as an athlete's performance in a long-distance run where data from previous runs can be analyzed on a computer. In sports where marshalling competitors over vast areas can prove impractical, GPS data loggers can be installed in each vehicle or attached to belts in order to confirm that participants indeed passed through the specified route in that particular competition.

A GPS data pusher takes a more active role. It constantly sends out its location to a receiver via radio or cellular network connections. Delivery and taxi companies usually make use of this system to keep track of their vehicles. It can also help recover a stolen vehicle by activating the GPS tracker, transmitting its location and movements continuously until the authorities arrive.

Then there are GPS data pullers. Not as popular as the GPS data pusher, this one works passively. It is always on, but requires a query before it sends out its location.

Some GPS receivers and GPS equipped hardware such as Notebook PCs and Handheld devices may be used for both navigation and tracking.

GPS is basically a positioning system that utilizes signals from a constellation of about 61 Medium Earth Orbit satellites to define exact position with a small circle of error, and from this you can determine location, speed, direction, and time duration. These satellites orbit at 11,000 nautical miles above the earth and transmit signals that can be detected by anyone with a GPS receiver, anywhere around the world! In order for it to work, GPS is comprised of three segments. They're known as the Space Segment, the Control Segment and the User Segment.

With all the three segments working together, we can now see how each segment plays a major role in locating and tracking GPS receiver's accurate position. The whole principle behind it is pretty simple. The GPS receiver is the device that we hold on to or the device that is attached to a moving vehicle. This device serves as what its name implies - a receiver that receives information from GPS satellites. The GPS satellites on the other hand, work as transmitters. They constantly send out signals towards the earth for GPS receivers to receive. But what kind of information does the GPS receiver really receive?

This is where it becomes clearer as to how GPS really works. The GPS receiver needs to know two things to properly determine its location on Earth. It should know the location of the satellite in space, and it should also know how far away the satellite is from the receiver.

To find out where the satellites are in space, the GPS receiver needs two types of information from the satellites. The first one is called the "almanac" data which contains the approximate positions of the satellites in space. Every GPS satellite continuously sends out this information for receivers to pick up in which each receiver then stores this information so it can plot the orbit and location of each satellite it detects. The second data the GPS receiver receives is the corrected and exact position data which is also called the "ephemeris" data. The "ephemeris" data is only valid for 4 - 6 hours so constant updates from the last GPS segment comes into play. The Control Segment is the facility that tracks every GPS satellite in space making sure that the updated location data of each satellite is sent out to the GPS receivers.

With this data, the GPS receiver now knows where each satellite is. The next thing that it has to know is its distance from each of the satellites. Remember that the location of the satellites have already been determined. Now each satellite sends out a "pseudo-random code" along with its status message. This "pseudo-random code" is a timing code which is generated by both the GPS satellite and GPS receiver. This GPS receiver compares the two codes to determine the difference in timing. This difference in timing is multiplied by the speed of light to get the distance.

Each distance measurement is also dependent on the GPS receiver's clock. Because the GPS receiver's clock is not as accurate as the atomic clock that synchronizes the GPS satellites, further correction for the distance information is needed. To get a more accurate reading, the position of the GPS receiver can then be calculated by intersecting distances from multiple satellites. Three satellites are required to determine a 2-dimensional position and four or more are necessary for to determine a 3-dimensional position.

While GPS sounds like a wonderful thing, current GPS receivers are not useable in areas where GPS signals from the satellites do not reach. These are underground structures, tunnels, underwater, or in heavily fortified facilities that can block GPS satellite transmissions. Even some modern concrete and steel buildings block the signal.

GPS accuracy depends on the GPS receiver used. Some receivers lack error-correcting capabilities, but most are typically accurate to within about 15 meters from the actual location. Some of the latest receivers may come with some form of error-correcting capabilities such as Differential GPS (DGPS), which brings the accuracy to within 5 meters or Wide Area Augmentation System (WAAS) which can raise accuracy to within than 3 meters.