Quite simple question.
This is a quick look of Beltane, a province of my fictionnal country :

Let me zoom to a random mountainous part of it :

I'm using Adobe Illustrator (a layer for each relief colour) and wonder how to make relief shadows ?
I found tutorials to create them from a scratch using Photoshop, but to you think it is possible to create them from pre-existing relief to make it more realistic ?
(like in this real exemple : http://upload.wikimedia.org/wikipedi...cation_map.jpg
of a part of Alsace in France)