Air

Air is the absence of a block. Due to its ability to be located on the map anywhere above or below ground, it must be treated as a block by map editing software.

As one would expect, Air is totally transparent, fills any space which does not contain a block, and cannot be affected, except by its replacement with a block. Looking directly up at ground level through air, is the sky. The sky is blue, and features thematically blocky renditions of clouds.