Zone generators create zone map independly, and Land generator mix neighbor zones to proper relief blending. Zone generators produces multilayered heightmap and blocks map: Base layer - inpenetrable lower layer, bedrock, lava, etc. Optional resources layer - some underground diggable treasures or just empty blocks, so it is possible to explore caverns (needs testing). Main layer - ordinary diggable dirt, sand, rock. Optional additional layer - temporary stuff like a snow, thick grass, ash, Zerg creep, probably water (needs testing). I want play with 3 layers (Base, Resources/Empty, Main) in this milestone.