via http://www.reddit.com/r/space/comments/37fx8t/magnificent_view_from_space_shuttle_endeavour_in/

"Interestingly, from 500 km up, you can only see about 20 degrees around the Earth in any direction. That's just about 6% of the Earth's circumference.

If my lazy scratchwork is right, in terms of area, you can only see about 0.08% of the Earth's surface from 500 km up."