Minecraft wiki entry for Sky_dimension, associated text: Originally, the Sky Dimension was hidden within the region 0 (Overworld) code. However, starting in Beta 1.9 Pre-release 3, it was given its own region: Region 2, with Region 1 being the Nether. However, Sky Dimension chunks stopped spawning within its region, they would generate in the Overworld on Multiplayer servers. This is most likely due to an issue with map generation and saving causing Sky Dimension chunks to save over Overworld chunks rather than being made in their own, separate map files like the Nether does. If a world with Sky Dimension chunks is brought from multiplayer to singleplayer, the area of the chunks will always be Plains biome, even if snow generated naturally on the ground.