no idea where it's from I've seen several different resolutions of this map and I think I saw it on the official sites.. but while I'm reading DnD books and in the past would have loved to play it (and have played a lot of DnD comp games, read the rules online and read bestiaries online etc) I've not actually played it so I''ve never bought any books..
http://www.wizards.com/default.asp?x=dnd/frx/20031019a
it seems to come from "Underdark supplement" according to this webpage (the acutal map on that page is much smaller in resolution though).
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