I think this mod is awesome, but it lacks a way to make safe places.
I would suggest making some tile irreplaceable by the creep, so we could just pave the base border and let the creep florish outside.

Good idea! I'm thinking at a minimum it needs to be concrete. With stone brick, the creep can take root in the cracks and crumble it to dust. That would mean, then, at least for Krastorio 2--concrete, hazard concrete, refined concrete, refined hazard concrete, and black/light reinforced plate.

I downloaded your code and started working with it and for now the creep ignore any tile with walking_speed not equals to 1.

but for now it doesn't work properly

EDIT: it works, I need just a little more testing and then i'll send you the change

I made it work, but I'm not that good at Factorio modding.
It needs a review from someone more experienced than I am.

Where can I send you the changes?

I've already done it and am testing it. :)

oh, ok, awesome.
It will surely be better than mine