MinecraftServer.java:182

            if (j == 0) {
                Layer[] layers = new Layer[2];
                layers[0] = new Layer(Environment.NORMAL, 0, 4, 10, 20, null);
                layers[1] = new Layer(Environment.SKYLANDS, 48, 4, 16, 0, null);
                world = new WorldServer(this, new ServerNBTManager(new File("."), s, true), s, dimension, i, new LayeredWorldProvider(layers)); // CraftBukkit
            }