Biome



According to Wikipedia, Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems.

In Minecraft, from the Halloween Update onwards, this means different areas with different heights, temperatures, humidity ratings and foliage colors are created.

Before the Halloween update, when a map was generated it got a theme of either Snowy or Grassy. After this update, a single world includes all themes in a logical fashion determined by the biomes graph.

A demonstration can be viewed here.

Pre-Update Saves
Worlds generated before the update will not be changed, but the grass color will be altered. However, any new chunks generated (by the player moving outside of the current world's bounds) will generate biomes, just as The Nether will be generated when you first enter it.

Biome Types
There are 11 Biome types: (Note: these names come from Notch's notes)

Biome Screen-shots
These screenshots were made by editing code in Minecraft's java files, creating worlds made up of only one Biome. This was done consecutively with each Biome type and their screen-shots are collated here. The original topic is on the Minecraft forum is here.

Remaining Work
Remaining work on biomes include variable elevations in certain biomes (flat elevation in desert biomes, etc.) in addition to improving the border between arctic and tropical biomes.

Also, snow currently does not "fall", meaning that once snow or ice has melted or been mined, it will not regenerate.