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[darknation]

So, I just noticed you can place walls right at the edge of the map down in the caverns...

Does this stop beasties from wandering into your cavern space? Is it possible to completely seal them off from the outer world for a, uh, *sterile* cavern experience?

Seems a little bit... too easy, somehow.

[KittyTac]

I won't do it because I need beasts for my arena.

[Fleeting Frames]

Yes. You can do it aboveground too, by placing raised bridges on map edges.

The task is simplified by capturing wild animals, and then pitting them into sealed pens so that new animal groups won't enter the map while you're nearby, but I know some just wait until the cavern has less dangerous creatures and wall then.

Mind that with bridges, flying beasties can still enter, and with both walls and treetops walking beasties can walk in from those.

[PatrikLundell]

My standard protocol is to wall off caverns at the edge while keeping a small section on each edge where I leave a single tile wide strip outside the wall and have an airlock to allow desirable creatures in (and I build minecart repeating menacing spike traps in the airlocks as needed to eliminate FBs). Cavern lakes require some extra effort, but I deal with them as well (mmm magma...).
I consider capture neutralizing of the caverns to be too exploity for my taste (other people have other tastes), so I do the building when benign creatures are around, observing their movement to pull the builders out as the critters start to leave. Of course, I sometimes don't have much choice when those blasted spheres camp out of reach in a cavern lake.

It can also be noted that as you build your walls, critters can spawn/enter at the top of those walls until you seal them against the cavern ceiling.
Since regular wall construction at the surface map edge is blocked, you have to resort to obsidianization if drawbridges aren't enough, unless you want to build floors on every level and build a drawbridge on top of that.

Since DF has a limited sky height, it is possible to block off the air space of the embark with walls as well, but the default height is fairly large (15 levels?).

[Dunamisdeos]

I legit did not know about the raised bridge thing.

If you lower the bridges, can you then allow things to spawn on the map? Also, what about caravans?

[PatrikLundell]

If you block access you block caravans, of course. There has been some speculation that very limited entry space for caravans can increase the risk of getting bugged caravans as well.
While I haven't tried, I have no reason to assume lowered bridges should block access.

[Thisfox]

I currently have 3 and 4 z-level walls around my upper cavern edges, but not all of them are right up against the edge, and the ones that are even a few tiles apart from the Edge now all contain forgotten beasts, steaming and dusting and flaming at the impenetrable walls, while dorfs on the other side happily farm mushrooms without a care in the world. It's a little tricky when lakes span the distance (they have odd water pressure) but so far they haven't spawned forgotten beasts, so I guess they're not much of an issue.

If you do wall off the surface, how do you deal with the Merchant waggon fleets? Do you just choose not to have them arrive?

[Fleeting Frames]

That's the deal. Nothing enters, nothing leaves - expect through eerie glowing pit. Convenient when you need to quickly run a test fort for few years; I have a macro for testing that seals it all off and sets up food stockpile, tavern, gathering zone, etc - previously used mainly for figuring out evil clouds available in a biome, till PatrikLundell made that pointless with his scripts.

Iirc old ocean-walling off tests had cases where migrants also arrived from the boundary of ocean biome in the middle of map, which could be blocked by statues.

[darknation]

Interesting. Thanks guys.

[PatrikLundell]

It's not that hard to block off cavern lakes as well, provided you can make at least one magma safe minecart, although two level deep lakes have caused me to leave a single tile gap at the bottom so far. A task for a future fortress will be to see if that process can be improved to leave no gap.

There are two reasons I don't want to have FBs outside of my cavern protection walls:
1. They kill off the interesting creatures that I may want to capture.
2. The remains of all the uninteresting critters the FBs killed contribute to the FPS draining fortress item clutter.

If you don't intend to actually let critters in selectively, there is no point in leaving room between the wall and the edge (unless you enjoy returning back to look at the FBs again and again as some kind of freak zoo).

[gchristopher]

@PatrikLundell do you know offhand if there's a per-tile "valid map entrance"-type flag like there is for surface invaders and caravans? I know that there was a flag applied to surface-pathable edge tiles at the moment of embark to determine valid edge tiles for caravans/diplomats/invaders/etc.

I was wondering if you could you toggle on and off things entering the caravan by manipulating the edge tile flags with dfhack?

[PatrikLundell]

No idea. I've never dealt with such flags. If they exist I would assume they would be stored in the tile structure, though.
When it comes to the surface path mapping, I don't think it's absolute, just a starting point (supposed to lead to low FPS when screwed up by massive pit mining, but I've never tried that), as I think people have been able to get caravans enter on constructed floor up in the air (I may be wrong and these have been used for leaving only, though). Given that cavern and surface critters definitely can enter on top of constructed floors/walls it's definitely not an absolute for cavern critters.

I know from my own experience that caravans can enter at map edge tiles that do not have wagon access to the trade depot (in my case I crossed a stream to build my fortress, but had only a single tile wide path over the water. More than half the edge DID have wagon access to the trade depot, though. Presumably some initial path logic used the embark wagon location as the target. I'm not sure 'D' showed access or not, though, as I usually use that only when I suspect trouble, and in that case it was immediately apparent what the fix had to be).

[Fleeting Frames]

There might be such a flag, supported by things like sometimes migrants rising out of ocean biome boundary on complete island embarks.

Iirc the worst case I've heard of was being sieged from the middle of fortress, but that was pre-DF 2012 iirc.

[gchristopher]

Yes, there is definitely a flag in the tile data for surface edge tiles. Also, yes, it does not respect caravan pathing at all. I tried restricting the flagged tiles to just a few to force caravans to spawn in that location, but then all the invaders only appeared there too, including goblin ambushes. (I MISS AMBUSHES!!! )

IIRC, caravans respect the flag, but diplomats do not, and you will still get diplomats sometimes spawning in weird random unreachable locations?