Biome map is a way Minecraft generates biomes. In fact, biome map is a two-dimensional array of biome ids inside every chunk.
To be able to change this map, GenerateBiomeMap callback is called after the landscape generation is performed and before cover and decorations generation. See Callbacks for details. Inside this callback you should call World.setBiomeMap to set biome on the coordinates and World.getBiomeMap to retrieve one. Note that these methods are available only inside GenerateBiomeMap callback. Also, you should pass coordinates inside the specified chunk. The coordinates should be inside these bounds:
var minX = chunkX * 16 var minZ = chunkZ * 16 var maxX = (chunkX + 1) * 16 - 1 var maxZ = (chunkZ + 1) * 16 - 1
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