Minecraft wiki entry for Server_level.dat, associated text: Others have read and modified the map's data by simply accessing the raw byte array in the datafile file. To do this, the player would decompress it, make changes to the bytes where the byte array is stored, and then compress it again. Since the player is editing it raw, the player must keep the first 344 (14E in HEX) bytes intact. The next 256×256×64 bytes are where the byte array is stored. Additionally, it is also possible to alter the spawn location coordinates this way if the player knows where to look: there are 3 integer values starting at byte 284 and thus overwriting the next 12 bytes (3 integers) allow the player to change the spawn location.