Factorio Forums

In many situations, it is not possible to connect a wall to a diagonal cliff. Because of this, it is not possible to seal off your base completely using walls, because a gap of one tile remains:
In the case of the above screenshot, it is possible to walk through that gap and that gap cannot be sealed by a wall. Also, biters are able to pathfind through that gap.

I believe that this behavior is unintended. One would expect a tile to be either sealable with a wall or be blocked by the cliff. Due to neither being the case in the situation in the above screenshot, it is often hard to completely seal off your base with walls without any gaps that biters can pathfind through.

Thanks for the report.
In next release, new walls will extend towards cliffs same as they already extend towards water tiles. It still doesn't guarantee tight seal, but it'll be much less likely to leave space big enough for player or biter to slip through.

As far as I can tell, the issue is fixed, now. Thanks.

After some further testing, I have discovered that the issue is not completely fixed in 0.16.31. The situation in the above screenshots seems fixed now, but in the following screenshot, it is possible for the player (but not biters) to move through the gap:
If you want, I can also post my savegame of this situation.

Although the wall blocks the player most of the time, if you run into the cliff in a certain place and then change direction into the gap, it is sometimes possible to run through the gap. But you will likely need several attempts for it to work. Out of about 70 attempts, 20 of my attempts were successful.

Before testing, after upgrading to 0.16.31, I tore down the wall and rebuilt it, so that it would extend as far as possible to the cliff. I did this because you said that the fix only works for new walls.

Reopened on reqeuest.

I am not sure why this was reopened.

posila wrote:... It still doesn't guarantee tight seal, but it'll be much less likely to leave space ...

I had asked for the thread to be reopened because I wanted to make sure that you were aware that your fix did not fix the issue completely, but only 90%.

For single player games, I guess that the remaining problem is not much of an issue, since biters seem unable to pathfind through the gap. However, for PvP games, I guess it could be a serious problem if it is possible for players to simply walk through the walls of their opponent's base.

Now that my bug report has been filed as a known issue (and not a "resolved" issue), I am happy.