From XKCD a completely brilliant flow chart helping you determine how old a map is. There are amusing references to Narnia and radioactive spiders mixed in with accurate historical changes (What’s the capital of Micronesia? Kolonia or Palikir?).
Click it to get the big version, and really look at it.
My favorite real question is:
(Number of Yemens) + (Number of Germanys)= ? (possible answers are 2-4).
Seriously, read the whole thing.