OK - if I don't quit staring at clouds I'll never get this map going. So - what I decided to start with:
Picked an intricate cloud, dropped it into PhotoPlus 11, and dialed the threshold up and down til I saw something interesting - looked like a nice sheltered harbor.
Did three slightly different gaussian blurs, each thresholded to about the same outline. Stacked, then set the top two to partial transparency. Merged. Found all edges. I usually drop back to PhotoPlus 6 or 7 for that step - it gives crisper edges. This found an aliased edge, with some funky gray artifacts. Well enough - thresholded that to get back to a simple b&w layer. White is going to be land, in this case.
Took the original cloud, grayscale, placed beneath the edge layer. Keeping that for elevations, maybe. Flood erased white of the edge layer, leaving just coasts. Kind of thick for my usual style of one-pixel coastlines, but could be useful if I do an overall view and a zoom-in. Gives me leeway to smallify the whole thing if I want later - the present 3072x2304 may be a tad big.
### LATEST WIP ###
Copied the B&W edge layer and contiguous flood filled my ocean with a nice unsaturated medium blue. Now to decide how many of those internal onshore edges need to be lakes and how many need to be erased. All the offshore bits look fine as islands. There's a few artifacts of the aliased edging that need to be erased no matter what. When I first fooled around thresholding this cloud looking for some likely randomness, there were a bunch of pixelly N-S and E-W artifacts at the coasts. Might go back to that if I need some piers later - this IS a harbor of some sort :-).
Naah waitaminnit - always getting ahead of myself - need to delouse the edge layer before I fill. Some of the Carto Guild styles expand certain layers under edges so, say, water shows under aliased shore. I work a more pixelly style so it's fine to have exactly sea then exactly coast, then exactly land. but I do doctor the generated shorelines to get rid of too-square corners, indistinct ?peninsula-or-islands?, and most little lakes. That'll wait til next post.