For four hours of work, that's a job well done. It is fun, I enjoy the icons you used. It does make things clear without needing to word it out.
The ocean is good.
One thing for such a quick map that could have been done differently I feel is the type of brush used on the land. Maybe a grainy brush, that gives a more ground feeling.

Gimp is fun. I like making free brushes for it. Though, I'm without a computer for the month, so it would be hard to give tips from my phone. One thing I can type now is:
Try different brushes at different opacities, and swipe the same on over the same places several times, then a different effect takes hold. I have no clue if that makes sense, but that one helped me with creating better mountains.
Also, Brightness and Contras button is your friend if drew something with pencil and scanned it. (Try putting the pencil sketch layer as multiply, 2nd > Brightness -Low -90ish and contrast -high +65ish. 3d add a ground layer beneath that layer. The multiply causes all the white to disappear from the sketch and the B/C for the lines to pop.)

Hehe, anyway, if you figure that out, it's quite nice