This is a script that transforms a black and white simple drawing into a map like image with grass and sea. I tested it only on my machine, and it take several seconds to run and create a reasonable looking figure. All my tests where tried on a 500x500 image with 200x200 dpi resolution.
My machine (the only one I tested this on) is Lenovo edge. It has a i3 processor (don't remember the exact model) and 6GB of RAM. I run Ubuntu 13.04 and gimp 2.8.4 on it.
How to use.
Place the plugin in your plugins directory and give it execution permission.
In Linux, the direction is
~/.gimp-x.x/plug-ins where x.x stand for the version number.
cd into your plugin directory and run there
chmod +x grass_and_see_texture.py
Comments and ideas will be gladly accepted.
Now, restart gimp, a new menu element, named "carto" should appear, with one member of the sub menu, "make grass and sea".
Create a new image white white background and paint (in black) on it the general shape of the land you want. fill the area with black coloring and apply the filter.
Edit: I updated the version:
1. It is possible to turn on/off the water creation.
2. The texture is more sharp.
3. Changed the color a bit
4. Small islands and and strips of land are kept.