Many aircraft broadcast information about how accurate their navigation system, which is almost always GPS, is at any given moment. The GPSJam map aggregates that data over 24 hours in time bins it into a hexagonal map. Green hexagons show where more than 98% of all aircraft who flew through that area reported good navigation accuracy. Yellow hexagons show where between 2% and 10% of aircraft reported low navigation accuracy. Red hexagons show where more than 10% of aircraft reported low navigation accuracy.

Data is pulled from ADSB Exchange.