Creating an Aerial Landscape

First, make a new document, 1000x1000 pixels, as usual, white background.

Go to Filter > Render > Clouds and apply them in document.

Next go to Image > Adjustmens > Curves... to increase the amount of contrast in the image, making the light areas Whiter and the dark areas Blacker. You can see what my curve looked like to the left here.

Now I'm going to select the dark areas. With Black as my foreground color, the easiest way to do this is to choose Select: Color Range. You can see a portion of the Color Range Dialog box to the left I had the Fuzziness Slider up to around 76 and the portion of the image that will be selected appears white in the preview.

After clicking OK in the Color Range Dialog, I made the edges of the selection softer by feathering the selection a few pixels (4) with Select: Feather

Within the selected area, I applied the clouds filter again. These areas are going to be the water eventually and the clouds filter will provide some value variety.

Now use Image > Adjustments > Hue/Saturation command to colorize this area. With the settings in the example, and the colorize box checked I was able to get a pretty good aqua color. Your image should look like this:

Now, to give our sea water a little surface disturbance, go to Filter > Distort > Ocean Ripple. I used Ripple Size:2 and Magnitude:9. You can see the effect

Now let's go to the terrain. Press CTRL+SHIFT+I to inverse the selection and apply a Filter > Render > Difference Clouds. the difference clouds will give us highlight and shadow areas in the landscape, making the land appear somewhat three dimensional, having hills and valleys.

Use the same Hue/Saturation command with these values: Hue: 131, Saturation: 78, Lightness: -35

Next I gave the ground some texture by applying Filter: Noise: Add Noise

Continuing to add texture to the dry land, I next applied Craquelure, one of the Texture Filters. Craquelure mimics a high-relief plaster surface, producing a fine network of cracks that follow the contours of the image.

Here is the result.