Superflat is an option when choosing world type. When chosen and generated, the ground will become completely flat (excluding villages). The world has a high spawn rate for Slimes and Villages. All other Overworld mobs, excluding squids and wolves, can be found here as well. The superflat world consists of 4 layers: a layer of grass, two layers of dirt, and a level of indestructible bedrock.As of 1.4.2 the player can choose from a selection of preset worlds such as: water world, bottemless pit and tunnelers dream.
A player might be able to survive in this type of place since the Villages produce some saplings and wheat. However, you need to find one first—just because the spawn rate is higher doesn't always mean you'll spawn in one or right beside one.