Some maps of the land of mathematics? This question is motivated by a little anecdote. I was at home teaching some secondary school math to a relative. At some relax time, he glanced at a book I had over the table - it was some text about analytical number theory that I had recently bought, second hand- and I  explained him that that was an area of mathematics quite arcane to me, that I'd like to learn something about it in some future, but I had little hopes... 
He looked puzzled for a moment, and then asked me: "But, wait a moment... You don't know all the mathematics?"
This happened months ago, and I'm still laughing. But also (and here comes the question) I'm still thinking about how to make some picture of this issue: the big extension of "the land of mathematics", in diverseness and ranges of depth - and the small regions that one has explored.
I was specifically looking for some kind of bidimensional (planar?) chart, perhaps with the most basic/known math kwowledge in the center, and with the main math areas as regions, placed according to its mutual relations or some kind of taxonomy. 
(I guess this should go in community wiki)

The Princeton Companion of Mathematics is a good resource. The mathematical atlas is good as well. The size of the bubbles are directly proportional to the amount of research activity in each area. This MO post might be useful also (looking at real world applications of arxiv areas).
