Okay, so it was suggested that I post something that discusses a little of the process I'm currently developing to create coastlines in GIMP, as an alternative to the random coastline method presented in RobA's famous Regional Map Tutorial. This little mini-tutorial assumes some familiarity with GIMP and with RobA's tutorial (what I know about GIMP, personally, I learned primarily from using that tutorial).
So, first off, what's the purpose? The idea behind this process is that sometimes you're working with a map where you want a little more control over the appearance of the land in the map than the use of the rendered clouds will produce. You might know that there are specific features you want to have--some of the possibly quite small--to appear in the coastlines and landforms of your final map. So... you need a method that will still help you produce some level of a realistic, fractalized appearance relatively quickly, but afford you that level of control.
Enter the Jitter feature.
I found that with judicious use of the a brush on Jitter can have the effect of roughing up a coastline and giving it an interesting appearance. Some times I go in with a very fine control, but here's a quick method that will produce results that you can then fine tune to reach the results you're looking for.
Step 1: The simple coastline
We start with a basic, simple-looking coastline.
It already has several key geographic features that we want to maintain. We've got peninsulas, islands, and a narrow isthmus connecting two larger bodies of land. (Here, black is land, and white is the sea.) We want to preserve these features, but with a fractalized looking coastline.
To start, we need to invert the colors. (We'll want the black to represent the sea and white represent the land.) To do this, go to Colors > Invert.
Step 2: Stroking the Selection
Beforfe we proceed, make a copy of the layer, in case we do something wrong, and want to revert to an earlier version. I do this after every step.
Next, we want to use the Wand tool to select the entire black region of the map. This will select everything that is part of the sea. After you have the black region selected, Invert the selection by going to Select > Invert. You will now have the entire white region selected. We select the black first then invert because if we tried to select one of the white regions with the wand tool, we'd miss several of the other white regions when we perform the Stroke action next.
Now, before "Stroking" the selection, we need to set up the brush we are going to use. Using the Brush tool set on circle 5 or 7, set the foreground color to either white or black. (I used Circle 5 set to black for this example, but you can use any shape you'd like.) Using white will build on the existing land, while black will carve out of it. I chose black because I had a couple inlets I liked that I wanted to preserve. Next, set the Jitter level. To do this, on the Paintbrush menu, check the box next to Jitter. You'll need a moderately high Jitter--the higher the Jitter, the more variation in where the brush will paint. Here, I used a setting of 1.75. I also set the spacing on the brush much higher than the default (here, 100). This helps to prevent a solid but squiggly line from being the result.
Finally, with our brush set up, we're ready to Stroke. Go to Edit > Stroke Selection. Make sure the check box/radial button for the Paintbrush is selected. This will ensure we use the settings on the brush that we just set up. Hit Okay and watch GIMP work it's magic.
Before we unselect anything, our screen will look something like this:
I'll proceed in the next post... but it may be a couple days before I can get this updated.