Double width roofs?
Have roofs with a width of at least two:
AAXX
AXXA
XXAA
Double width roofs?
Have roofs with a width of at least two:
AAXX
AXXA
XXAA
You need to place at least one object of a specific room type into the room and may at the same time not have objects of other room types or objects that are considered industrial. (Most work tables, except some kitchen tables) Ecopedia has a list on what objects are for what room.
Day 38 on a long-term roleplay server, world is set to the highest value suggested by strangeloop. Makes one's individual contributions to pollution pretty miniscule even if they wanted to.
So, 1 km²?
You need to start the server manually, it's one of the UI features.