It was created from hundreds even thousands of photos taken by many photographers, pablo. Autopano sponsors these projects. The first one they did was of Paris, France. I think the paris project was better explained.
The soft can handle just about anything you throw at it. If your interested you should look into the soft... As I said, it really works, and well too. I use it with my 3D stuff in various ways also.
EDIT
If you were curious about how massive a working file is, and how hardware deals with it, I have no idea. I suspect the system they put this together on cost a lot more than my PC.
Who knows though. I never tried anything that large