[davidw]

Compiled from hiking maps? In places like Egypt, his first example? My guess is that there aren't a great deal of hiking maps for the Sahara desert...

They're compiled, I think, from whatever they can get their hands on. It's interesting to see borders, for instance, where there is clearly a difference in the data available. Switzerland, for instance, seems to have really good data:

http://maps.google.com/maps?f=q&source=s_q&hl=en&...

Austria... not quite to the same level of detail.