Why Is My Phone GPS Inaccurate?

Phone GPS becomes inaccurate when the signals from satellites are blocked, weakened or reflected, or when the phone has too few usable signals to calculate a reliable position. Most errors come from the environment around you, not from a fault in the phone.

Signals are very weak

Satellite signals travel more than 20,000 km and arrive extremely faint. Anything that sits between you and the sky weakens them further: roofs, ceilings, dense foliage, even a thick bag or a car with a metallised windscreen. With fewer satellites heard, the position estimate becomes less reliable.

Reflections confuse the timing

A receiver assumes each signal arrived in a straight line. In cities, the signal may bounce off glass and concrete before reaching the phone. This is called multipath. The longer path makes the satellite seem further away than it is and pushes the position off by tens of metres. See urban canyons.

Indoors is difficult

Walls and roofs absorb much of the signal. A phone indoors often falls back on Wi-Fi and cell-tower information, which is coarser. This is explained in why GPS does not work well indoors and how phones use Wi-Fi and cell towers.

Cold start and slow fixes

When a phone has not used GPS for a while, it needs to download satellite data before it can calculate a position, and that takes time. Phones usually speed this up with network assistance, but in poor conditions the first position can be rough.

Drift and filtering

To keep the dot from jumping, phones smooth readings over time and may combine them with movement sensors. This helps while walking, but when you stop or change direction the estimate can lag behind or wander a little around the true point.

Other factors

• Location services turned off or set to a low-accuracy mode
• Battery saver restricting location updates
• A phone case or mount shielding the antenna
• Atmospheric effects that slightly delay the signal

What helps

1. Go outside, or near a window with a view of open sky.
2. Allow precise location for the app, and keep Wi-Fi on.
3. Wait 10 to 30 seconds for the reading to settle.
4. Look at the accuracy circle on the map; if it is large, the position is uncertain.
5. For a doorway or entrance, zoom in on the map and place the marker by hand rather than trusting the dot.

For the difference between how close a reading is and how finely it is written, see GPS accuracy vs precision.