Every square where an aircraft was heard by a receiver feeding Skydex. Measured, not predicted: no range rings, no aerial height, no guess about what a station ought to reach.
4,000 squares of 0.5°, from 85 ADS-B receivers, over 31 days of history. Shade follows how many sweeps found traffic in each square.
Private aircraft never reach a square. The grid is built from the same privacy-filtered snapshot the map draws, and which antenna heard which square is not published either.
Squares are 0.5°, roughly 55 km, five times coarser than the ships grid. An aircraft at altitude is heard for hundreds of kilometres, and a finer grid would draw a precision the measurement does not have.
Live views are a different thing and stay where they are. tar1090 shows what is flying right now, and it does that better than anything we would write. What it cannot show is coverage: readsb measures range from one configured point, so a receiver on another continent draws a lobe across the ocean rather than a second area, and it writes no contour per receiver at all. This grid comes from the aircraft positions instead, so it needs no coordinates from any station. Open raw tar1090 or the live network map.
A single receiver shows its reception rose and its range record on its station page, where the owner has entered antenna coordinates. A grid per receiver does not exist on this band yet. The station leaderboard lists them; the ADS-B network page says how to add yours.