How this is measured

Every five minutes this page's recorder asks adsb.fi for every aircraft inside a box from 24°N to 50°N and 125°W to 66°W, which takes in parts of Canada, Mexico and the sea. An aircraft counts only if a volunteer receiver heard its position in the last minute. OpenSky Network, a separate set of receivers, is counted every fifteen minutes as a cross-check: .

The streaks show where each aircraft's last measured speed and heading carry it over five minutes. They are drawn from one measurement and repeat until the next.

The ghost sky is where aircraft were at the same minute seven days earlier, from the daily history adsb.lol publishes under the Open Database License. It is a different set of receivers from tonight's count, and its positions between two sightings are drawn on the line between them, so the two numbers are close cousins, not the same measure.

A takeoff is an aircraft heard on the ground within three nautical miles of an airport and then heard in the air within twenty minutes. A landing is the reverse. Aircraft no receiver hears on the ground are missed, so both are undercounts.

Road distances are from OSRM routing on OpenStreetMap roads, airport to airport. Airports are from OurAirports.