What that the hatching looks like, up close.
The most recently posted set of geomorphs were scanned at a pretty decent resolution, so it’s possible to enlarge things to see the detail. Whether that’s for better or for worse, I’m not sure.
Hatch and other fine detail is done with a Sakura Micron 02 pen. Wall edges and other detail with a Paper Mate Flair M. Water is Prismacolor – True Blue.