the "difficult" part is always the layout/idea - after you got that down, this style is easy to replicate. Start of by making a layer in photoshop for the outline of the land - then draw the outline with a pencil or hard brush. Then you can use the magic wand to select the insides (or just the fill bucket) - fill in the color for land (if you want it really pretty make a new layer for the fill and place that below the outline, this will make sure the color don't "eat" the outline) and then make a new layer, and start drawing in the shapes for mountains, repeat for high points of mountains, forests, lakes. Draw in rivers (remember they don't split, only come together, always take the easy route and move towards the sea (or a lake)). Then add cities and towns and put in roads good luck, and remember if you want help while you work - make a WIP thread inhere and post your progress