In response to a couple of requests, I've put together a video tutorial that can walk you through how to make a terrain map out of an astronomical object like a nebula, the Milky Way, or another galaxy. I suggest you watch it with closed captions on.
Well, I've only ever tried a city map once, and that was back in my early days of mapping. There are some stunning city maps you can find on dA, and I understand most of the processes that goes into making them, but making them right is a long and arduous process; it'd be more of a series of video tutorials than a single one.
Not quite; it's a question of time and priorities right now; I've got a pretty big project I'm working on at present, along with a doctoral thesis I'm trying to finish (plus I have five kids, a full-time job, and a part-time job). Teaching myself how to make city maps and then making a video tutorial on the subject is not very high on the priority list, but it's something I'd like to try once life slows down a bit.
That's an excellent question! In this case, I did not make the nebula; it's a real picture of a real nebula taken by the Hubble Space Telescope. I haven't created my own nebulas, but it's certainly possible. In fact, many of the terrain techniques for fantasy cartography rely on randomized cloud filters, which could easily be adapted to make a nebula.
this is the sort of thing that my brain tends to obsess about... even the patterns formed by grass clippings on a driveway after a rain storm can be quite amazing when viewed in the context of highly compressed fluid dynamics and natural erosion. i'm seldom without my camera and i'll photograph natural shapes that i find all the time... cracks in the sidewalk are beautiful when seen as rivers transposed over other landscapes...
a few years before i was introduced to DA, i took a photo of a leaf in a parking lot and by using very basic techniques began to create well over 700 different patterns by diving deeper into the replicated shapes and textures...in fact one of the first posts i made to DA was a thin slice of a photo of looking up at a tree and branches then mirroring the image then replicating it several times which transformed it into an arching cathedral ceiling... even now, i look for smaller patterns in bark and lichens