I found this little guide on how to make Vintage maps (I followed a link I found here, but could not find the link again). Since I could not find the path I found it on, I can’t give credit. But whoever you are, thanks!
While it is built for Photoshop, it helped me use Gimp. So, being useful to me, I share with yawl:
https://www.designcuts.com/tutorials/create-a-vintage-treasure-map-in-photoshop/
https://www.designcuts.com/tutorials/create-a-vintage-treasure-map-in-photoshop/
Yes! That’s an awesome tutorial. All my maps and my NPC cards were made using those techniques. Has some cool free resources as well and as John Williams said: The steps are not that fancy so it’s possible to do it with other tools than photoshop, too. BTW I use PS Elements (not the fullblown one) myself.