What is GPS?

🛰️ How GPS Works

All GPS devices—whether car sat navs, handheld units, or smartphones—rely on signals from orbiting satellites to determine your location.

💡 Professional-grade GPS units (like those used by surveyors) can also access ground-based radio signals for enhanced precision. This is called Differential GPS (DGPS), but it’s not available on consumer-level devices used by geocachers.

Learn more about DGPS

🌐 GPS Satellite Systems

There are three major satellite navigation systems currently in operation:

• GPS (USA): Managed by the U.S. military and used worldwide. Popular brands like Garmin and Magellan rely on this system.
• GLONASS (Russia): Offers similar signal capabilities but with different satellite coverage. Many newer Garmin handhelds support GLONASS.
• Galileo (Europe): Operated by the European Space Agency. It’s still being rolled out but will be compatible with existing GPS devices.

📡 Satellite Coverage and Accuracy

The U.S. GPS network consists of over 30 satellites orbiting Earth at an altitude of 20,200 km (12,600 miles). Each satellite takes about six hours to travel from horizon to horizon.

Most GPS receivers have 12 channels, allowing them to connect with up to 12 satellites simultaneously. To calculate your position accurately, your device needs signals from at least four satellites. The more satellites it connects to, the better the accuracy.

📍 For more details, see the section on “Features of a GPS.”

🔄 Combining GPS and GLONASS

While GLONASS has fewer satellites than the U.S. GPS network, it provides comparable accuracy. Devices that access both systems won’t necessarily be more accurate, but they will acquire a position fix more quickly by connecting to a broader pool of satellites.

See which Garmin devices support GLONASS