Field guide · updated context
GPS accuracy is useful, but never the whole navigation plan.
Selective Availability was the deliberate degradation of the civilian GPS signal. The United States ended that practice on 1 May 2000, producing a major improvement for civilian users. A later 2007 policy decision removed the requirement to build the capability into future satellite generations.
A receiver can provide a valuable position estimate, but the displayed number is not a promise that you can locate a small object to the nearest foot. Satellite geometry, obstructions, atmospheric conditions, receiver quality, movement, and map data all influence the result.
What changed when Selective Availability ended?
The 2000 decision stopped the intentional global degradation of the public signal. Contemporary comparisons recorded a much tighter spread of positions after the change. Those historical measurements explain why civilian GPS became more useful for navigation, surveying support, emergency response, transport, and outdoor recreation.
The improvement did not make every receiver equally accurate, and it did not remove the need to understand uncertainty. A position shown on a screen is an estimate derived from signals, processing, and the information stored in the device.
How should climbers and hikers use coordinates?
Use a GPS position as one layer of a navigation system. Before leaving, record a waypoint for the trailhead, camp, junction, or other meaningful feature. Compare the device with your map and the terrain around you. If the destination is a small object, navigate first to a distinctive landmark and then finish with a short distance and compass bearing.
- Keep the receiver where it can obtain a clear view of the sky when practical.
- Allow the position to settle instead of relying on the first number displayed.
- Cross-check the reading against contours, ridges, drainages, trails, and known landmarks.
- Carry spare power and retain paper-map and compass skills.
- Use more than one reference point when locating a concealed object.
A practical offset method
For a cache, emergency point, or other small target, navigate to a visible landmark first. From that landmark, follow a measured distance on a stated bearing. A second bearing from another known feature can provide a useful cross-check; lines that meet at a broad angle generally give a more helpful fix than nearly parallel lines.
Accuracy is not the same as reliability
Even a good position estimate can be misapplied. A device may show an impressive number while the user is reading the wrong coordinate format, using an old map datum, overlooking a route change, or moving through terrain that blocks signals. Treat the GPS as a decision aid, not as permission to continue when the route, weather, or group condition says otherwise.
For current navigation practice, combine this historical background with the map, compass, and GPS classes, the navigation seminar notes, and the site's guidance on using map, compass, and GPS together.