GPS navigation systems are invaluable in travel, helping us find specific addresses and locations in unfamiliar areas. These systems need to be very accurate in order to do their job, but just how accurate are they?
When commercial GPS receivers were first released, they were much less accurate than today's units. Typically, an early generation GPS receiver could only locate your position within 100 meters. That kind of accuracy might be OK if you're looking for a large building or landmark, or need to know what part of town you're in, but you can forget looking for, say, a specific car in a parking lot.
The thing is, this 100 meter accuracy wasn't a limitation of the GPS network, it was an intentional obfuscation set up by the government called Selective Availability. No, this isn't a conspiracy theory: in the early days of GPS, the military didn't want unfriendly nations to be able to have the same advantage as the US when it came to GPS, so they programmed the satellites not to give the most accurate positioning data to non-military GPS units.
A system called Differential GPS was eventually developed to improve the accuracy of GPS units to around 10 meters. DGPS used a network of reference stations to more accurately calculate the GPS receiver's position. This made the system much more suitable for precise navigation. After the year 2000, the government disabled Selective Availability for commercial GPS units, and the accuracy was improved to about 5 meters.
However, while plenty accurate for most users, this still wasn't good enough for the FAA's standards of aircraft navigation, and a new system, called the Wide Area Augmentation System, was developed. The WAAS works similarly to DGPS, but can offer GPS precision within 1 meter. WAAS has some disadvantages, however, such as only being available in North America.
Today's GPS navigation receivers are much more accurate than early models, and with systems like Differential GPS, can typically offer accuracy within 10 meters. This level of accuracy is great for vehicular navigation, even when trying to find specific addresses. It also makes activities like Geocaching possible with commercial GPS receivers.
GPS systems will likely continue to become more and more accurate, with other continents developing systems like the North American WAAS, which makes <1 meter accuracy possible around the world. Some day, we may very well see GPS accuracy within a few centimeters.