This is part 1 of a number of parts, probably 3, that will add up to a very nice effect. In part 1 we're going to lay the basic earth, clouds, and a meandering river.
Off we go...
Step 1: Create a new layer and apply the "Clouds" filter to it, under FILTER > RENDER > CLOUDS.
Step 2: Duplicate the clouds layer you just created by right-clicking it and selecting "Duplicate Layer", and set the top layer's blending mode to "Color Burn".
Step 3: Merge the two layers by clicking the small arrow in the top right corner of the "Layers" panel, and then "Merge Down".
Step 4: Duplicate the merged cloud layer. It will look something like this:
Step 5: You should now have two duplicate layers and the background. Double-click the bottom layer, and in the "Layer Style" interface, click "Pattern Overlay". Load the "Nature" patterns by selecting the down arrow next to the pattern thumbnail (see image below).
Now select the green grass pattern, and set the scale so that it looks accurate with the make-believe height you're viewing your landscape from.
Set the blend mode to "Screen" and you should have a basic grass/cloud image as seen below.
Step 6: Now that you've got the earth layer looking spiffola, select the other cloud layer that you duplicated in step 4, and set it's blend mode to "Screen". What you should have now is a basic cloud layer on top of your cloud/ground layer. Anything you add between will appear below the clouds.
ADD A RIVER
Step 7: With the bottom grass layer selected, select the "Pen" tool.
Make sure that you have a nice blue selected in the swatch panel of the toolbar. Then, somewhere right off the canvas (zoom out until you can see the edge) click with the pen tool and draw a squigly line across the whole width or height - whichever way you decide your river should go. Once you go off the canvas on the other side, loop around and draw in the other side of the river. Your image should look something like this:
Step 8: Double-click the shape layer to bring up the "Layer Style" panel. For my babbling brook I set an inner shadow with a 10px distance and 7px size, at a 137 degree angle. I also set a texture (under the "Bevel" section). The texture I picked was "Streaks" with a 50% scale, but try different ones to get a watery look that makes you happy inside. Set the bevel depth to 1.
Your river should look pretty badass at this point. If you want to make it look a little more realistic, add a dark brown centered stroke of 1px with a blend mode of "Multiply". This will give a little dirt between the edge of the land and the water.
Here's what I have so far:
In part 2, we'll create some hills, valleys, houses, and other elements to give our map a little action. Stay tuned.
If I follow exactly what you have said, It doesnt work. do I need to add transparency, or what? if so, to what layer? im totaly confused. my clouds dont go nice and chunky like yours either, even when Im holding down Alt. also, what size canzas did you make it on?