Uncharted Atlas is a Twitter bot that generates a new fantasy map every hour. The brainchild of glaciologist Martin O’Leary, it uses algorithmically created terrain that is weathered by water erosion, a process he details on this page (All Over the Map’s post explains it in more human-readable terms). As Martin writes:
I wanted to make maps that look like something you’d find at the back of one of the cheap paperback fantasy novels of my youth. I always had a fascination with these imagined worlds, which were often much more interesting than whatever luke-warm sub-Tolkien tale they were attached to.
At the same time, I wanted to play with terrain generation with a physical basis. There are loads of articles on the internet which describe terrain generation, and they almost all use some variation on a fractal noise approach, either directly (by adding layers of noise functions), or indirectly (e.g. through midpoint displacement). These methods produce lots of fine detail, but the large-scale structure always looks a bit off. Features are attached in random ways, with no thought to the processes which form landscapes. I wanted to try something a little bit different.
The code is available for playing with, and apparently other people are doing just that. Another algorithm—one that linguists should find fascinating—generates the place names.