Gabon shows up when you have too much pollution, and Santa stays away when there is too much pollution.
A problem I ran into was that my pollution kept going higher and I couldn't figure out why. It turned out my water was heavily polluted and I didn't realize I should have been building water treatment plants. If you go into build mode and use the question mark tool you can get information about a building/square of land. Do this on a polluted area and see what type of pollution you're having.