What Triggers Cave-ins?

[Eleazar]

At first i had the impression that as long as you didn't mine out an entire 11x11 square you would be fine.  But i still got a cave-in in my very large room with strategic pillars to avoid 11x11 spaces.  So how is it calculated?

[Shinzy]

piece of wall supports the roof 5 blocks away (in like a circular pattern, bit like the sunlamp's lightning area)
can you show screenshots? it'd be easier to tell what caused the cavein!

[Goo Poni]

I agree with Shinzy, a screenshot of the caved-in area will help us explain it. The rule is that any tile not supported by a wall within 5 tiles of it will collapse.

Pulling an image from another thread, this shows what the support pillars should look like, optimally.

[igpron]

Guess that explains why my rooms in the shape of a sunlamp effective area are fine.

Haven't made larger rooms than that, yet.

[_alphaBeta_]

It may not be judged as "worth it," but an overlay helping the player visualize the support system would be kind of nice. With larger rooms, I'm always counting squares in lots of directions.

I suppose this could be as simple as a 5 tile "circle" template or stamp, colored like the planning tool, that attaches temporarily to the cursor. The player could quickly visualize the consequences of mining out a wall when a square in question has no other structure within the radius. Would save lots of counting.

[milon]

The center tile in an 11x11 room is not supported by a wall.  You can get away with 10x10 (or even 10x50 if you like) since the nearest wall is no more than 5 tiles away.

[Eleazar]

piece of wall supports the roof 5 blocks away (in like a circular pattern, bit like the sunlamp's lightning area)
can you show screenshots? it'd be easier to tell what caused the cavein!

Sorry, the room is rather different now, screenshot time is past.  But that answers my question, i expected the support range to be square, not circular.