If you're interested in creating your own maps like Rosettas lava and water map, you'll need to take a look at the following article: Map Editing. It covers the basics of how maps work and how to modify them!
Hm. This is still confusing me.
I un compress it with 7zip, open it with a hex editor, and i have no idea what to edit and how. I tried changing some things but it gives me an error when i load it up in minecraft.