How do I build/dig on the edge tile of a map? My dwarves are walking around the edge of a moat; I assume invaders will too.
According to the DF wiki, "You're not allowed to wall within five squares of the edge of the map... but this rule has more loopholes than the US federal income tax code."
Some tactics allowed by DF that may apply to this problem:
1) You can build floors all the way to map edge. A floor built over a ramp that is then removed, removes the ramp. Removing ramps at map edge may stop the ability of foes to path-find into your map.
2) You can smooth un-mined stone and then fortify it even if the tile is at the map edge.
3) You can build a drawbridge at map edge. A raised drawbridge acts as a wall. This won't stop flying foes, but it works against normal goblin sieges.