It uses UK government LIDAR data to reflect the actual skyline, so it knows whether there's a building or a hill blocking the sun.

Caveats: - Outside LIDAR coverage (most of Scotland and Wales) it falls back to a synthetic horizon (less accurate). - Trees and recent developments (post-2022 or so) may not be in the data, and some address placements could be off (geocoding via OSM).

Feedback on the shading model especially welcome.