[Award Winner] Using GIMP to Create an Artistic Regional RPG Map

[Yellow Eagle]

Sorry.. I wasn't clear.. I continued onto the "Land Clip" step to get the colour levels, but didn't get the effect I wanted, so I kept moving back and forth between the two steps to see where I went wrong. I managed to get the Land Noise (Filter/Render/Clouds/Solid Noise) done right, with "Layers:Overlay" from the Layers Dock, and then created a New Layer (Land Clip), fill type:White; Lighten Only. Then I adjusted the Colour Levels to Output(71) (as in tutorial.. I know the actual number can be different). What I get is white "land" and gray "sea", with no cloud-like "landmass".

here is what I've been able to do so far:

[Seretur]

Ah, that could do it. You skipped a step:

Now invert the layer (Color->Invert) and blur the image (Filters->Bur->Gaussian Blur) The amount of blur will determine how random the final coast will be. The larger the blur, the more random the coastline will be (in the blurry area). If you have a well defined coast already (like here) use a smaller blur (50px). If you have a poorly defined coast (as is the case when using a random coast technique) make it a large blur.

If you want to preserve the mini-inlet northeast of the big bay thing ( I'm incredibly geographically literate, aren't I? ), but randomize the rest a bit, try a 50px overall blur, select the inlet area with the lasso, and Select->Invert. Blur that (50-100px) and the inlet should be preserved, while the rest of the coast is a little more random.

If you think your coast is just fine exactly how it is, you don't need to worry about this at all. This step is just to randomize the coast. If your coast is well-defined, and you like it, feel free to skip the Land Noise and the Land Clip, and go straight to the Land Mask.

(( In the future, adding a new post with the attachment would be most convenient for everyone. Now it looks like I'm double posting ))

EDIT: While I was typing, I was looking at your outline JPG. A lot of the definition got lost when you traced it, and I wouldn't recommend leaving your land layer how it is unblurred. If you want it to look closer to what you originally drew, try this:

Click on your Background layer, hide everything else.
Using the magic wand tool, select the sea.
In your Land layer (or a new one if you don't want to destroy what you've got), fill the selection with black.
Invert the selection (Select->Invert), and fill the new selection with white.

This way, it will keep your original coastline exactly (or almost). Then you can leave it unblurred, if you like.

[Yellow Eagle]

I originally just duplicated the background layer to make a second outline, then filled in the land w/ black and sea w/ white. This latest "tracing" was an attempt to simplify the procedure . In the end, I'm going to use your suggestions, and basically skip the first segment and go straight to the "Land Mask" step after defining the land/sea.
Thank You for the advice.. BTW, I edited my post before I realized you (Seretur) already responded

[Jacqui]

I've rendered my difference clouds and marged it with the blurred mand mask layer above the dirt - you've then said that in the layers dialog, you have to have a wider band of white than black.
I have a "Layers, Channels, Paths, Palettes, etc." box but where is the dialog?