I've played dice-based RPGs since around '85 or '86, and any gamer knows how that can lead to maps. Sometimes the idea is just a general campaign world, no maps needed as such; other times though, it's pretty specific, and a map is absolutely indispensable.
I've always been one to make maps by hand, but a few months ago I had an idea for a meta-setting. It wasn't for any specific game world, but rather as a backdrop for any games that you want to put there -- much like outer space being a general background for Star Trek, Star Wars, Firefly, etc.. In this case, it happened because I'd been breezing through YouTube videos and asked myself "What if the Flat Earth theory were right, and there really were an ice wall where we believe Antarctica to be, and the whole thing were just a vast conspiracy?" (And: "Just what would Antarctica looke like anyway, if I were to turn it inside out?")
One thing led to another, and suddenly I had trillions (literally) of square miles to work with. I documented the storm of setting-ideas in a very rough and basic description (70+ pages of details, plus 7-8 more pages of just 5-10 word notes scribbled in to get back to, and loads more that are just a few quick words on paper or in my phone's notes and still awaiting transcription). I put in a pathetically simple map from MS Paint (it might as well have been drawn by your average 5 year old), and wasn't thrilled with that, but didn't really feel "the itch" to fix that just yet.
Then I made that one fateful mistake. I asked another question: "What sorts of adventures might occur on an infinite plane of ice, with world ponds of all sorts of game worlds strewn about, though separated by thousands of miles of -70° darkness?" Well, I answered that with a few reasonable possibilities, and then added a throw-away idea just for fun; help Sonic and Princess Zelda save Princess Peach from Donkey Kong, who had kidnapped her under duress at the orders evil Wario-Robotnik-Ganondorf-combination.
That idea kept gnawing at me. While I daydreamed at work, I imagined a romance novel developing out of it (mostly along the standard historical romance formula, though with what I hope is a leaning toward some of Sherrilyn Kenyon's "Dark Hunter" ambience). Then I was stuck with the bug. I needed to write the story out. Here I am, 140+ pages into my femslash fanfic (one that I never intended to write, mind you, yet have it set up in a very nice .pdf with a hyperlinked table of contents and footnotes and so forth... plus 16 pages of 5-10 word notes to expand upon [and I already have the outlines for two prequels and a sequel stuck in my head]... <grr-sigh>), and I realized that I needed to map the place out for myself and for any potential readership. That's when I started digging around for simple and easy mapping software.
GIMP was a bit too bloated with [admittedly beautiful] bells and whistles for my learning curve preferences. I settled upon AutoREALM, and have just begun expanding/transferring into Inkscape, though I also grabbed Paint.net to experiment with. I think that the map is coming along decently (though my writing is stalled out because of my diversion with the map).
### Latest WIP ###
UPDATED 2018 / 07 / 10:
Light World - select-all copy-n-paste.jpg
The mapping software came up not long after I had introduced an NPC of my own devise, an Immortal Wombat from a sort-of Gamma World / Ninjas and Superspies setting. This was my third mistake. These two items combined to remind me that I'd never gotten around to mapping his home world (I had a couple of ideas for it; one based upon everting Australia, another based upon everting Pangaea [though lately I've been thinking to go with Pangaea Ultima, instead]), and since I'd been mapping out the other idea's world already anyway...
So here I am now, working on one map and juggling the beginnings of another (if I can just manage to get my hands on some software to invert Stereographic projections). To that end, I've recently grabbed Krita, Blender, and Unity, and can only hope that something will perform that function well. Even if not, I'm sure that it will make for an educational experience, and they could always be useful for later projects.