How does Google know the terrain and elevation?

Question

Google Maps

The question is not entirely about IT, but suddenly someone knows.
Sports apps like Endomondo, Runtastic, Strava, etc. often show elevation data.
Google Maps has the same feature in some countries. The cyclist types in an address and looks for the best route in terms of incline, number of climbs, and so on.
How is such data collected on such a scale? How to download them in a computer-friendly form? Is there a database of this information already collected somewhere - or (unlikely) every startup collects it on its own?
Thanks

Answer 1

Google uses all the terrain models available to them.
Where there is nothing better, SRTM data is used (this data is obtained from a radar survey). Many countries use higher resolution data published by local mapping agencies (for example, for the US, this is the NED terrain model ).
There are also other height models - ASTER GDEM (obtained from stereo images), AW3D30 (free terrain model obtained by the Japanese space agency from a more detailed commercial one).
Here is my own data comparison of SRTM 1-arcsecond (top) and AW3D30 (bottom).

Answer 2

generally GPS, but can buy

Answer 3

https://ru.wikipedia.org/wiki/Shuttle_Radar_Topogr...
https://wiki.openstreetmap.org/wiki/SRTM