Seed (level generation)

Seeds are referred to the "Seeds" option when you are generating a new world. Implemented in Minecraft Beta 1.3, seeds make it so you can choose what type of world you spawn on. Minecraft players have the option at the beginning of the game to name their world, and add a "seed". This can be a series of numbers, letters, or symbols. A Seed works as a base number for a random generation of a map, in older versions when maps were randomly generated the seed was picked randomly. Using a seed should always result in the same map, but spawning locations are chosen randomly. Please note that while putting the same seed usually results in the same landforms, results may vary by system. The generation seed gives an average over the entire map, not always the exact same map.

Examples
Note: Please move to x:0 and z:0 and documenting the map from there as the spawn location differs.

1 - A series of small islands, some which include small pools of water, and large amounts of sand/clay.

2 - Lots of stone mountains/canyons visible.

3 - Flat islands of sand.

4 - You are spawned in the middle of a desert.

5 - Flying stone cliff above water. Open air dungeon.

404 - Map with a sinkhole at the coordinates -25, 65, 15.

21ab - Middle of an ocean with many islands.

100 - Desert.

666 - Big desert.

87654321= Small grassy patch, surrounded by snow and ice.

1234567890 - Large flat grass areas.

l33t - Floating islands.

DIM-1 - Large overhangs, plenty of floating islands, several 'mountains', and a large snow biome with many Pine trees.

Mayor - Floating land structure near spawn.

Minecraft - Lots of wood near spawn, a beautiful world in general.

Glacier - lots of floating cliffs but just a cool world

9000.1 - lots of floting sand and water falls

omgjizzfacelol - Puts you in a desert with a zombie mob spawner to your left. (Not a joke)