Campaign mapping documentation?

I've had a look around, and I'm not able to find any guides for campaign map modding. The closest I can find is threads from 20 years ago, and the readme/faq that ships with LMM4.

Thankfully it seems as though the tools necessary to create a new campaign map are still available - but I can't make any sense of them. The instructions seem mostly to have been written by and for people who already know how to do the work, and for decades-old computer systems.

It is clearly possible to make new campaign maps for MTW - if someone could point me in the right direction for finding the necessary information, or how to get started, I'd appreciate it!