Minecraft wiki entry for History, associated text: The next 32,768 bytes contains the block data. The block order is YZX. Every 1 byte is equivalent to going up vertically along the Y axis. After 128 bytes, the height limit of the world is reached, so we move South 1 block along the Z axis and repeat. After 2,048 bytes (128*16) 1 column of the chunk is finished, so we move East 1 block along the X axis and repeat. In most programming languages, this is just a basic 3d array blocks[16][16][128] ([x][z][y]). To reiterate, every 128 blocks is a column on the Z axis, every 16 columns is a row on the X axis.