Biter (and other enemy) behavior question

[Targa]

Hey all. I was under the assumption (wrong now, I know), that unless enemy nests were within your pollution cloud, or very close to the edge of it, that they wouldn't attack your base. In my current game I don't have any biter bases that close (there was one, but I killed it). Yet I still occasionally get attacked. The console says their evolution is at 0.164 (I've only ever seen small biters and worms so far). So my question is, how far away from my base and outposts do I need to clear before I get to the point where they stop attacking? Do they have a "maximum travel distance from nest"? Or will I get random attacks no matter what? Thanks!

[DaveMcW]

They will send out groups to colonize empty areas of the map.

To see where they want to go, press F4 -> always -> show_enemy_expansion_candidate_chunks.

[MalcolmCooks]

Also: If they have established a nest underneath your pollution cloud, it won't show up on your map until your radars have re-scanned that area, which can take a very long time

[Targa]

Also: If they have established a nest underneath your pollution cloud, it won't show up on your map until your radars have re-scanned that area, which can take a very long time

Bingo! Little suckers snuck in under the radar. Thanks!