Minecraft wiki entry for Terrain_features, associated text: When features are generated, they can spill over into neighboring chunks that have been previously generated. Thus, a tree at the edge of the generated world (and probably visible only via external tools) may be overwritten by a lake before the player reaches it. It is also theoretically possible for two worlds generated with the same seed, from the same version of Minecraft, to differ slightly depending on the players' travel routes, because the chunk generation order may determine which of two conflicting features overwrite or suppress the other.