Surfaces should tell their cost

I know it says it costs "1" concrete, iron, or steel, but does it really only cost 1? Or does it cost 1 per some amount of area? If so, what is that area? Is it the smallest map square, the biggest map square, the digging map square? Maybe even per 100 tiles like pipes and belts?

Note: I was unable to find any information about surfaces in the wiki.

I figured it out by using the copy/paste function but I stand by my earlier suggestion

It's one per tile.