Well... At the exported size, squares are 85px in size, which makes it a little bit hard to tile automatically in GIMP (since so far I haven't figure out how to make a 42.5 px grid). What I do is I make an 85 pixel grid and then I copy and offet it a couple times. The resulting squares are "irregular" by one pixel, but they line up across the whole map (which isn't the case for 42px squares). 84px per square would be a great size (easily divided by 2 or 3). Thanks for your reply!