Here’s my tutorial for how to make a map in the style of this: http://www.cartographersguild.com/showthread.php?t=4753
Special thanks must be said for jezelf, from whose tutorials I borrow frequently and liberally.
Before you start, I suggest you download these brushes and such that I’ve attached here and a good parchment texture, (http://www.andreas.blicher.info/imag...land_paper.jpg), and you will most certainly want Wilbur for a likely unnecessary step that adds a bit of realism for those not so well-versed in geology, such as me.
First off, open a new file in Photoshop. Let’s say, a 2500 x 2500. Duplicate the background and run a difference clouds filter (or, alternatively, not make a new layer and run clouds, doesn’t make any difference; see step1 below).
Then we’ll add a threshold layer via the little icon at the bottom-right (see step2).
Go ahead and keep the standard 128. Now we can use the burn tool on the clouds layer to make a good continent shape. Burn will cause the black to expand, while holding Alt down while using the burn tool to make it retreat. For now, let’s assume the black is land. So we’ll screw around with the burn for a while and make a fair shape (see step3).