Explanation for tile IDs

Refering to the LMU map data.
I can’t seem to figure out anything asides from non-terrain and water tiles start at index 5000 for some reason.
I tried looking at the lmu2png code and it seems to have its own tile id system and I don’t feel like going into that.
I think I can figure out chipset passability by myself (they look like just simple bitmasks) but I’d appreciate if I could get an explanation for that too.

(For the record I’m looking at lcf2xml output, incase that for some reason translates IDs)