Thanks for sharing those. The popup on hover says "Elevation: [...]" so I think you're right that they're approximating grade by using a height database. It cou

Thanks for sharing those. The popup on hover says "Elevation: [...]" so I think you're right that they're approximating grade by using a height database. It could be OSM-based if enough contributors are supplying lists of (lat, lon, elev) GPS coordinates from journeys they take. It's also very possible that they're using the public domain dataset from the Shuttle Radar Topography Mission (SRTM)[1] in 2000 -- probably with some cleaning to eliminate large spikes due to trees and buildings. [1] https://wiki.openstreetmap.org/wiki/SRTM https://wiki.openstreetmap.org/wiki/SRTM