One word answer: Photoshop. Well, okay, and practice, I suppose. But thanks!
The sand might be. I found the texture with a Google image search, so I'm not sure. The rocks/mountain, not at all. I drew those myself.
First off, thank you. Second, and I hesitate to admit this, but I did not draws those myself... not entirely, anyway. You see, I... I can't draw, so instead I... uh,
borrow other people's work. I search the net for all kinds of stuff, like big drawings or concept art pieces, down to tiny things like cool-looking sci-fi/fantasy icons, and I rework those heavily to fit into my maps. Not just this one, but I've done this with a few other of my maps, for example my
Wyrmenwaerve map. I know this might be considered "cheating", but as you can see, I do not claim all these pieces of art that I include in my maps as my own. And professional artist do this all the time, especially with concept art, so I guess it's okay, right? Anyway, to answer your question, you can find the original works by googling "fantasy desert city" or similar, or going on Pinterest and search with the same terms.
Thank you. Who knew that (essentially) clicking Filter->Sharpen->Sharpen in Photoshop can make such a difference?
In terms of file-size, pixel dimensions or real life? And thanky.