I use the paint app, Krita, and the text I add in Inkscape. Both free and open source applications. The large map of the island I put together with a map I photographed in an old book, and then I simply zoomed in on the first map, and painted the details myself on this new rough and pixelised image, inventing new details that then again got more detailed when I zoomed in further.
There's no hint from the maps of the nature of the world I am building here. It is a medieval sort of world, but as magic is derived from sacrificing the living, the whole thing turns toward the bleaker end of fantasy.