Superflat

Superflat is a World Type, first introduced to Minecraft in Snapshot 12w01a, replacing the normal varied terrain of The Overworld with a thin flat layer of dirt.

The terrain consists of one layer of Bedrock, two layers of Dirt, and one layer of Grass; the surface of the world is completely flat and at height y = 4. Since the height limit (128) is unchanged, there is then slightly less than twice as much vertical height available to build above-ground structures as compared to a normal world. Mobs spawn as normal, including slimes; however, due to the lack of any overhangs blocking the sky, there is no “void fog” as would ordinarily be caused by being close to the bottom.

The Nether and The End generate normally; they are not flat. In order to create a superflat world in SMP, the level-type flag in server.properties must be "FLAT", instead of "DEFAULT".

Bugs

 * If one breaks the Bedrock barrier, then one can see that the Void has the same color of the sky when the Player is above y=0, but looks normal (black) when the Player is below y=0.
 * There is no consistent spawn point unless you have slept in a bed; you may respawn far from your previous location without anything in sight. This may be due to the lack of ground at the usual height of about 64.

Trivia
If you play a normal survival world with a superflat world, you can get dirt, rotten flesh, bones, bone meal, string, spider eyes, gunpowder, arrows, ender pearls, slimeballs, raw porkchops, raw beef, leather, leather armor, wool, raw chicken, feathers, music discs, stone (from creeper explosions), and furnaces.