More Map Layers

[Rabid Lemming]

For future mod-ability and maybe even current use I think it would be nice to see more map layers usable for construction. My ideal scenario they would look like this:

Underground / Underwater (maybe?)
On Land / On Water (water currently isn't treated as part of the map only an obstacle)
Above Land / Above Water (high enough to bypass normal land structures, could be used for more costly transport bridges over the top of areas)
Air (highest layer for aircraft to fly wouldn't likely have any blockages except for very tall buildings)

As part of the game having many layers, each object should be able to place no-build and collision areas in any part of these layers they want to. For example a drilling rig would occupy a space on land which is large and also a smaller footprint underground. A skyscraper would block everything from the land level into the air level.

[Arch666Angel]

You can already make additional surfaces. Mod examples:
viewtopic.php?f=97&t=25444
viewtopic.php?f=97&t=19178

[aubergine18]

There are also multiple render layers that can be used (wiki is a bit out of date but should be enough to get started): https://wiki.factorio.com/index.php?tit ... enderLayer

Also, I believe there are already several aircraft mods in the mod portal so flying is also possible.