How do you find out the format of the map files? Is there any form of source released or something? Do you just have to do a bunch of guess and check? I'd love to make a map editor, but I'm way out of the blue when it comes to finding the format of a binary file
The files are compressed. You'll need to unzip them with a program such as 7zip, then open the resulting file with a hex editor, then rezip in gzip form and rename to server_level.dat for it to be usable again.
Byte 320 is where the block array start. Its a 3d array with z starting at the bottom. I have made head way into making the map bigger as well as changing the spawn location but I will have to post those locations later as I don't have my notes on me right now.