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.
