OK, here's my question: How do you set up a bridge to be perfectly flat, but with no reference point (How do you create a floating platform that is level?)
Or you could just stack a bunch of boxes up then place on top of it then delete the boxes that should be accurate.
He asked for no reference, which I believe in turn would include the floor, as for the question I'm not quite sure though I believe when spawned it is flat already. You could spawn a bridge, save-quit float it, come back and build off of it resulting in your flat surface platform. Hopefully this helped.
There is a floor anywhere, on any map, that could be used as a reference. Even if it is a floating map outside of the map, you could still use the floor as a reference.
as soon as you spawn the bridge, it should be flat. save and quit like everyone else said. it should be perfectly flat. if not, then just do it again until it is perfect. EDIT: sorry. I didn't see your post
either way I'm only explaining what he asked for, which could help anyone else who is constructing a floating map. The fact that there is a floor is a dead give away to build off it my post is only an explanation of what he essentially asked in the first place.