Thanks Caenwyr! Argh seems that I'm on heavy fire to make a tutorial or giving tips
Alright here we go for the mountains : Those are hand-drawn with a graphic tablet (but in this style there's not that much tablet function used - just a very small controle pressure that's it, so that can be easily done by hand then scanned). Here's a quick one.
First draw a simple outline (here I used a small grungy round brush - no need to be too neat and clean for the style, that is intended to emulate some old 17th century style cartography mountains):
Then add "shadows" by simple curved hatching and a few dots:
Then add a bit of noise:
Once scaled down and put on a background with a dark brownish color you're done
Oh wait, now you just need to draw dozens more mountains
You can draw them all on the map or if you want to re-use them on some other projects, turn them into brushes. Here I use them as brushes. Basically I draw the mountains, keep a few individual ones and build up some ranges (horizontal, vertical, diagonal ones, in short/medium/long sizes) and build up the final ranges on the map with them.
Hope that helps