How Accurate Is a GPS Unit?

GPS accuracy depends in part on the signals received from satellites.

A GPS unit receives navigational data from the Global Positioning System satellites. Its accuracy depends on several factors including obstructions to satellites such as trees and buildings; proximity to military installations, atmospheric conditions and the type of unit being used.

Accuracy

Garmin, a leading manufacturer of GPS equipment, reports that modern units have an accuracy of up to 15 meters -- roughly 50 feet. This is adequate for many purposes such as general navigation, but it is inadequate for applications such as navigating a missile, piloting an airplane or surveying a building's lot. However, there are ways to enhance the data for better accuracy.

Assisted GPS

Assisted GPS uses wireless networks like cell towers to supplement satellite data to increase accuracy. Accuracy can be greatly enhanced when a GPS unit can locate its position relative to both a fixed location and the satellites that are sending data. As the assisted system develops, accuracy will become even greater.

Differential GPS

Differential GPS uses fixed locations to adjust data to increase accuracy even more to less than a meter. The Federal Aviation Administration and Department of Defense have developed a sophisticated differential system to aid aircraft and military applications. Their system is generally not available to the average user.

References

• Garmin: What is GPS?
• Maps-gps-info.com: GPS Accuracy - How Accurate is it?
• SkyTel: Assisted GPS