Quick and Easy Land Sculpting in Photoshop
I came up with this technique on my last map as I've been trying to find a really quick and easy (and easy to remember) way to "sculpt" the land into hills and ditches and things.
1) First of all you take your base ground/grass layer or whatever and once you are happy with it, select it all and copy it.
2) Start a new image, paste your land layer to it and then define it as a pattern. Call it whatever you want, then close the image.
3) On your original image, create a new layer above your base land layer. Open up the layer style menu for this layer, add a pattern overlay (using the pattern you just made), and add some bevel and emboss using similar settings to the one in the attached image. You can play with it to get the sort of effects you want.
4) Take a low opacity (about 33%) soft brush and just begin drawing in your contours. It might take a bit of practice to get it took how you want it too, but it's very quick and simple.
I hope someone finds this useful.