Is it possible to capture terrains that are larger than 10x10km in Google Maps? Ie I’d like to capture larger areas like entire countries.
No, it is not possible. That would result in too much points or, by reducing resolution, a poorly detailed mesh, almost a flat mesh.
However you can get larger terrains by importing several pieces separately and joining them. There are arrows in the import window that allow you to easily place the view for that specific purpose.