I'm the guest blogger right now on the Chronicle Books blog.
I did a little self-cannibalizing of my own blog and works, and I also took the opportunity to dispel the myth of seeing the Great Wall from space.
Think about it. How ridiculous is that? The Great Wall is, what, ten feet across? Sometimes it crumbles and almost disappears into the landscape. It's not even as wide as your house, unless you live in a NYC railroad, in which case your 8-foot-wide apartment is probably in a large building that is way wider than the Great Wall but duh, cannot be seen from space.
Okay, sure, bring a telescope with lots of power and you can see anything. We're talking naked eye here.
I personally have not been to space to confirm all of this, and I think in China it's a "fact" that the Wall can be seen from space, but I went to a lot of trouble to look it up and NASA astronauts agree—nope, can't see it.