Why did civilian GPS navigation systems suddenly become radically more accurate overnight on May 1st, 2000?

The error was built into the signal

GPS satellites broadcast timing information that receivers use to calculate how far away each satellite is. With distances from several satellites, a receiver can work out its position. But for years, the U.S. military deliberately made the public signal less precise through a feature called Selective Availability.

The system added small, shifting errors to satellite timing and orbit data. Those errors made civilian position estimates wander, even when a receiver was working correctly. Military users, with access to a separate encrypted signal, could get more accurate results.

A switch, not a new satellite system

At midnight on May 1, 2000, the United States turned off Selective Availability. The satellites did not suddenly become more capable; the intentional errors were simply removed from the signal available to civilian receivers. Devices already in use could therefore calculate positions much more accurately without being replaced.

The change was dramatic because the error had affected GPS users around the world. Civilian accuracy improved from roughly 100 meters to around 20 meters under typical conditions, though buildings, terrain, receiver quality, and other factors could still affect a fix.

Civilian dependence changed the calculation

Selective Availability had been intended to limit the usefulness of GPS to potential adversaries. But civilian navigation was becoming valuable for more than finding a route: businesses and public services increasingly relied on accurate positioning, and ground-based corrections could already improve GPS for users who needed it.

The U.S. government concluded that keeping the deliberate error in place carried costs for ordinary users without offering enough security benefit. Turning it off made GPS more useful at once—from mapping and navigation to other location-based applications. The memorable part is how little had to change: a global improvement in positioning came from removing a hidden source of error, not upgrading every receiver.