This means your GPS signal is noisy, which may be:
- because your GPS module is not very sensitive or misconfigured
- because of the terrain (in thick woods or canyons)
- because it’s stored at the bottom of a backpack or pocket
- because of jamming (intentional or power lines)
Once you’ve excluded the physical causes and have reset your GPS (and rebooted the phone for good measure), if the track is still showing zigzags, you can set up filtering in MyTrails by using the
set kalman filter n hidden option, where n is the approximate nominal speed in m/s, for example 1 for walking, 8 for cycling.