surface data from Google Earth

[Maverick91]

Does anyone know how Google Earth arrives at its surface data? I know it's not the most reliable. It's useful enough for us for concept, though.

[heidib]

Aerial Photography is used, it's most likely 2-3 years old and comes from a 10M DEM. Not sure where the DEM is received from though. I know this works great for preliminary design but, I'd never ever use it for final design. It's usually off 2-3' no matter what I've noticed.