Every square where a volunteer AIS receiver feeding Skydex has actually heard a vessel. This is measurement, not prediction: no propagation model, no aerial height, no guess about what a station ought to reach.
1,067 squares of 0.1°, from 12 receivers, over the last 30 days. Shade follows how many messages arrived from each square.
This map does not show which antenna heard which square. A station page shows its own squares, and the maps draw a station on its 0.1° square, never at the antenna’s exact position.
This is the last 30 days, not right now. What the receivers are hearing at this moment is a separate view, with every vessel the upstream feed contributes filtered out. Open it here: the live network map, or the same traffic on the tiled map.
A single receiver draws its own grid, its reception rose and its range record on its station page, under Coverage. The ships ladder lists them; the AIS network page says how to add yours.