You will find as many GPS units on sale as you will find computer products on sale. Global navigation and positioning products are squarely in the high-tech sector and benefit (or suffer, depending on your perspective) from the same quick price drops as technology improves. Unless you are one of the people who must have the hottest new product, you can save considerably by buying the product that has just been surpassed.

You can also save money by purchasing packaged deals of GPS products. Say you are in the market for an automotive GPS navigation unit, you will probably need to purchase several related accessories. If you purchase a GPS navigation unit, a cigarette-lighter power adaptor, additional map software, a mounting bracket, and a custom faceplate, you will almost assuredly pay more than if you purchase a package that includes all of the accessories.

You can also find sale prices on GPS products in the usual way, by shopping around. Online retailers are always putting products on sale to attract customers to their websites. Shopping in this manner, you should have an idea of what you want and the specifications of products that suit your needs. Specifications may not be prominently listed but you should be able to find them with relative ease.

Specifications of Global Navigation Devices
GPS devices vary by frequency, processing protocols, software, error correction, and accuracy. Better devices use dual frequencies rather than a single frequency, Kinematic processing (On-The-Fly–OTF) rather than static processing, real-time processing rather than post-processing, and differential GPS (DGPS) rather than standard GPS. A devices antenna also plays an immense role in overall device performance, so make sure you buy a device with a robust antenna.

With the explosion of interest in the global positioning and navigation market, the number of suppliers for GPS products has also exploded. In addition to the retailers sanctioned by the major manufacturers of GPS equipment, traditional retailers and e-tailers are offering consumer GPS devices as well. There are literally dozens of companies that produce GPS products and hundreds of companies that sell them.

GPS devices are available in more and more forms, and with more and more accessories than ever before. The fitness market uses GPSs tracking and timing capabilities to measure distance and average speed for joggers, with the ability to plot a backtracking path for runners in unfamiliar surroundings. These devices are also being coupled with heart monitors and other health-related devices that make use of GPSs superior atomic timing ability.

You need not necessarily go to a dedicated GPS provider to find such niche devices. GPS is rapidly becoming a ubiquitous technology, and you can find GPS products marketed in other product categories, too. For example, you can often find GPS watches listed with regular watches, rather than having to search through all of the available GPS products to find them. In the strictest sense then, GPS suppliers are everywhere.

Dedicated, Respected GPS Suppliers
In the consumer GPS market, the two acknowledged leaders are Magellan and Garmin. These two companies put out more GPS devices, for a wider range of uses, than any other companies. They are both backed by large corporations who will likely be around well into the future and available to answer your questions and offer support throughout the life of your GPS device. They also offer extensive software support and mapping capabilities.

Global positioning and navigation systems are being used for an increasing number of scientific and industrial endeavors as well as for private, civilian use. The devices most people think of when they think of GPS are those designed and marketed for consumer use, like automotive navigation systems and handheld systems for use by outdoor enthusiasts. However, industrial use is so large that many large GPS companies have separate divisions for professional and consumer users.

The Global Positioning System is a product of the US Department of Defense and is not alone in Earth orbit. Russia has a system called GloNaSS and the European Union has a system that will be completed in 2008 called GALILEO. Collectively, these systems are called Global Navigation Satellite Systems, or GNSSs. There are other systems in place called Satellite Based Augmentation Systems (SBASs) that improve the function and accuracy of GNSSs as a whole.

A GNSS is set up so that a receiver on the ground will be able to make contact with at least four overhead satellites at any given time and at any point on Earth. The contacts are used to geometrically locate the receiver (and therefore the person operating it). The system can also be used to determine elevation as well as position. One quirk of the system is that it does not (at least for basic civilian use) register altitudes below average sea level.

Making Use of Global Positioning Systems
GPS receivers, for whatever uses, all operate in basically the same way and will be more or less accurate and reliable based on individual design and construction. The most accurate consumer models utilize differential GPS (DGPS), dual frequencies, and kinematic (or On-The-Fly) real-time signal processing. These systems can also use signal encrypting (known as Y-code) and have a host of other specialized features, the list of which is too long to enumerate here.

GPS technology is not static. Since the first GPS satellite was launched in the 1970s, the system has been constantly expanded, improved, and augmented to increase the overall accuracy of the system and its availability to industry and the general public. The system was declassified by the US Department of Defense (the architects of GPS) in the mid 1980s and the first consumer GPS receivers started hitting the market. By the systems completion in 1995, with the launch of the 24th satellite, GPS was already firmly established in the consumer marketplace.

The US DoD had introduced a program called Selective Availability which degraded the systems accuracy for civilian users, but that program was ended and consumer GPS units achieved accuracy to within 10-15 meters. There is a new program called Anti-Spoofing which ensures the military maintains the most accurate system, but advances in consumer GPS systems have lead to accuracies to within a few centimeters. These hyper-accurate systems are known as DGPS–differential GPS.

Overall system accuracy is relatively uniform. The differences between GPS devices are mostly products of the design and construction of individual receivers. Low-grade electronics and antennas coupled with bare-bones signal processing results in a receiver that is less reliable and less accurate. For the majority of people, standard GPS accuracy (to within 10-15 meters) is enough. However, reliability is a major concern so consumers should definitely shop for quality.

Buying for Usage
If you have certain uses in mind for a GPS device, you should look at models designed for your intended use. Automotive GPS and wilderness GPS devices vary significantly in their capabilities and in their ruggedness. Wilderness receivers often include features like a compass, a barometer, an altimeter, two-way communications, and an emergency beacon. Being stuck on a mountain in a snow storm carrying your cars GPS unit is not an ideal situation.

GPS units vary significantly by category and by capability within each category. All-purpose devices are good for a broad range of uses but devices targeted to specific applications are usually better within their specific realms. Though devices can be used for purposes other than those intended, you should shop for GPS units designed for the specific applications for which you are most likely to use them (an automotive GPS device for driving and a handheld device for hiking).

Within each product category, you will find entry-level models and more sophisticated models with enhanced capabilities. For most of a product category, accuracies will be relatively uniform but high-end models may make use of DGPS and advanced signal-processing for increased accuracy. High-end models will also usually have specialized or expanded features that make them better suited for their intended applications than models on the low end.

High-end automotive GPS units will often have greater and more detailed map coverage, advanced signal-processing to reduce errors, enhanced voice-command navigation, touch screens, and more extensive points of interest (like gas stations). High-end units designed for use in the wilderness will often have topographical maps, a compass, a barometer, an altimeter, weather reports, an emergency beacon, and two-way communications. Paying more for a GPS device is often well worth it.

The Top Manufacturers of GPS Units
The general consensus among GPS users (and this is reflected in the marketplace) is that the top two manufacturers of GPS devices are Magellan and Garmin. Both companies have experience that stretches back to the early days of the Global Positioning System, and accomplishments that allow each to argue their superiority. There are a number of smaller GPS providers that can be included as players in the GPS world but none that can rival the top two in the consumer GPS arena.