The screen begins empty. What you see builds over time, you are watching the sky draw itself. Each aircraft within 250 km of London Heathrow leaves a hairline trace, barely perceptible on its own. Individually these marks are near-invisible; collectively they accumulate. The approach corridors materialise as pale rivers converging on west London, the endless eastbound finals over the Thames valley, the stacked holding patterns above the Home Counties, transatlantic heavies descending in long arcs from the north Atlantic.

Colour encodes altitude: warm amber near the ground, shifting to near-white blue at cruising height around 10,000 m. Brightness is pure accumulation, the more traffic has passed through, the brighter the trace.

Data provided by The OpenSky Network. Refreshes every ~30 seconds.