Originally posted by jonnin:

your best bet is to run 10 or so.
open the map generator site and make 10 random maps with the crypts turned on, and nothing else to control clutter. see what the trends are for swamps.
Ive made 1 new map and continued 2 old maps since ML, not enough to say anything at all.

the streaks o swamp are nothing new, though. I had one map where it was literally 1-2 tiles running along an almost dry river for about 100+ tiles -- right thru the plains. It would spawn swamp mobs, but there were not even any trees apart from one small (5x5 ish) puddle at its biggest part.