Adding to the other answers, there are also -besides Photoshop, Gimp, etc- specialized tools to draw fantasy maps. The site mentions Wonderdraft [0], but there are a bunch of others though not all of them support using external brushes.
Some other tools in this space may be Watabou's tools [1], Azgaar's tools [2], Inkarnate [3], Mapforge [4], or quite a few more which you can find links to in this list [5]. Again: you could use these brushes with some of these; not all support external brushes.
Some other tools in this space may be Watabou's tools [1], Azgaar's tools [2], Inkarnate [3], Mapforge [4], or quite a few more which you can find links to in this list [5]. Again: you could use these brushes with some of these; not all support external brushes.
[0] https://www.wonderdraft.net/
[1] https://watabou.github.io/
[2] https://azgaar.github.io/Fantasy-Map-Generator/
[3] https://inkarnate.com/
[4] https://www.mapforge-software.com/
[5] https://www.mapforge-software.com/links-to-map-making-apps/