Environment is shared by every tile on the board — leave on random to roll one value for the whole map, or lock it.

Board size — rows × columns (each tile is 6″). Stored as the first two letters of the code (A=1, D=4, F=6, H=8), so DD… is 4×4 and DF… is 4×6.

Density — how much of each feature the board packs in.

Buildings — leave blank for a random amount (per the density above), or pin an exact number of separate buildings (connected groups of building tiles, Bnn). Each building is at most 2×3 tiles. Dropships — how many dropship tiles to place (default 1, stored as Znn when it isn't 1). Type S UFOs — how many small (2-tile) UFO ships to place (0 by default, stored as Ynn); each is a front + rear pair. Larger crash-site UFOs come from the UFO density above.