Where the network hears
There are now two maps for the ADS-B side, and they answer different questions.
tar1090 is the live one. It shows what is flying right now, it has shown it since the network opened, and nothing about it changes today. If you want to watch traffic move, that is still the page.
The new one is skydex.online/adsb/coverage. It shows where the network has actually heard something over the last month: a grid of half-degree squares, shaded by how often a sweep found traffic in each one. Nothing on it is predicted. There are no range rings, no aerial heights, no assumptions about what a receiver ought to reach. A square is lit because an aircraft was heard there.
Why the live map could not do this
We tried the obvious thing a year ago and it does not work. readsb, the decoder behind the aggregator, can draw a range outline, but it measures that outline from one configured point. For a single receiver in a garden that point is the antenna and the result is honest. For an aggregator taking feeds from England, Germany, Canada and Louisiana, there is no such point: pick Hamburg and the Canadian receiver draws a lobe straight across the Atlantic, claiming coverage over open ocean where we hear nothing at all. There is no per-receiver contour to fall back on either, because readsb does not write one.
So the outline has been switched off since August, and the coverage question went unanswered.
This grid takes the other route. Instead of measuring outward from an antenna, it records where the aircraft were. That needs no coordinates from any station, which matters more than it sounds: several receivers feeding us have never had a position entered, and the anonymous route cannot have one by design. They are all on this map anyway.
What it shows today
Four clusters, on two continents: southern England, northern Germany, Nova Scotia and New Brunswick, and the Mississippi delta. Two hundred and sixty-three squares, five days of history, about a hundred and sixty thousand recorded sweep-minutes. The collection started at the beginning of September, so the window fills out over the next few weeks.
Because the network genuinely spans an ocean, the map opens on a view where a single square is a few pixels wide. That is the real shape of a small network, and zooming in would hide it rather than fix it. So the page also prints the shape in words underneath: how many squares in each country, and how many out over water.
What it does not show
Private aircraft are absent. The grid is built from the same privacy-filtered snapshot the public map draws, so a private airframe is never written into a square, at any resolution, on any day.
Which antenna heard which square is not published either. The map answers what the network covers, never where a particular volunteer lives, and that line is the same one every station page holds.
Squares are half a degree, roughly 55 km, five times coarser than the equivalent grid on the ships side. An aircraft at altitude is heard for hundreds of kilometres and a finer grid would draw a precision the measurement does not have.
If you run a receiver, your own reception rose and range record are still on your station page, and the ships network has its own coverage map with the same rules.