The maps below were done going through a couple of steps. (Gimp 1.3 was used so there might be slight differences with your version of Gimp)
To create a new map, make the layers you want to show visible by clicking on the eye symbol in layer dialog box.
Go to the file dialog and Save a copy and give it an appropriate name and extension (preferably .png).
Gimp will ask a couple of questions about merging layers before saving, make sure to click on the [Export] button.
Another dialog will appear asking about the PNG options. The defaults are fine, except make sure to set compression to 9.
Open the file you just created and in the menu go to Image -> Mode -> Indexed.... Another dialog box will pop up asking for the number of colors you would like to use set it to 32 and make sure you select the No Color Dithering option before hitting the [OK] button. Note: Reducing the colors will bring the size of the picture down from 22kB to 6kB.
... further cooperation.
International organizations of Reformed churches
International Conference of Reformed Churches[?]
Reformed Ecumenical Council[?]
World ...