Currently the only way to create maps is either to use the built in generator while changing XML settings or by manually doing it with the Map Editor.

The maps are saved as GC3Map file along with a thumbnail image file:

• A GC3Map file is binary.
• 90+% of the content always changes on save even if you only change the map name. (compressed?)
• 7Zip recognizes it as a compressed Zip file, but can only find two folders named "Save.tmp" and "Description.txt", and nothing else
• Map hash is never the same even if content is the same. (salt seems randomized)

Maps uploaded or downloaded from Steam Workshop generate a "*wsdata" file. "gc3cwsdata" for uploaded, "gc3wsdata" for downloaded. These might be used for verifying map hashes as it is always the same file size no matter the map size.

So, so far I don't see a way on creating a valid GC3Map file through programming.