So I was futzing around with a world I generated a while ago, and found out if I move a tile north, and a tile west I can get a 3x6 map that has a bottomless pit, magma pipe, underground river, surface brook with tributary, a bit of soil, a bit of trees, red sand, 'other' features, and the entire map is coated in Obsidian.
The center of the map has the brook, nestled in a valley, with the sand and other features to the east, and the underground river, pipe, and bottomless pit on the west side.
Now I can't decide where to build the main bulk of the fortress.
The east provides a very nice and easy game, what with no irrigation needed [And indeed, I have already set up a temporary fort in the soft sands and the glistening obsidian there], but putting a fortress there would require large plumbing projects when I build a magma manufactory.
The west side provides a more interesting location, with the majority of the good features right nearby; I could build my sewer system, and a cistern, then should emergency arise the bottomless pit offers an excellent way of disposing of any excess water, magma, or FPS that I should have lying around.
I could always build in the center; but the last time I build a fortress directly under a source of infinite water one of my plans went awry and I ended up with naught but a single dwarf left alive, a child, sleeping soundly as the rumbling of the water caressed his dreaming, insane mind.
Where would you build?