Everything in the air over London

Methodology

ADS-B positions from the OpenSky Network, bounded to 51.25–51.70°N and 0.55°W–0.30°E. Aircraft are classed by vertical rate: descending faster than 2 m/s counts as arriving, climbing faster than 2 m/s as departing. Positions are proxied through an API route and cached for LIVE_CACHE_TTL seconds, so OpenSky is polled once per interval no matter how many people are watching. Coverage depends on volunteer receivers — this is what the network can see, not a guaranteed census of the sky.