I have started a new world from scratch with just random PS-clouds and I'm then trying to figure ways to create a world from there.
Basically I generated three layers with black/white render/cloud-filters and added these over each other by trying different transparency or blending options until I had a shape of greyscale topology I liked. The render/cloud-filter always renders the same scale of fractal which makes the over all distribution a little too even. So I scaled the top layer 500% and moved it around until I got som continent like lighter blobs on my workspace.
There was a lot of trial and testing in these steps, but I ended up with this.
The top adjustment layer enhances the contrast (in this instance I used /levels restricted to the upscaled top layer only) so the shapes become better defined. I then painted the adjustment layer-mask by hand with a broad soft brush to enhance where I wanted the continents.
Then I tried to figure at what level of grey I wanted the sea level to make the prettiest shape for continents. I used select/color range and picking one of the brigter areas and then moving the fuzziness gauge around until I was satisfied. I finish the selection and enter quick mask. In quick mask you can increase the contrast by tool of choice. I use levels here to keep some control over coastline antialiasing. I want it sharp, but not 2-bit-sharp which will end up with ugly pixelized edges when I use stroke on the coastline later.
Some manual painting and editing was done to remove unwanted islands and objects that crossed the edges from the selection.
At this stage I copy the landmasses and the seas to different layers so I can work with them separately from now on. The water layer here is tinted blue at this stage for visility only. The lakes are hand painted to a darker color in the tinting layer only because I want to separate them from the oceans. It is a good idea thing to save the continent selection to an alpha layer at this point.
I'll continue with Part 2 in this same thread within short. But don't wait for it. I'll be happy for all tips and comments on this part before the next is finished.