Yeah, erosion is something I still have to learn about! Thanks for your input, it's too late to change the rivers and coasts now but I'll read up on the subject and think more about it next time!

About the drawing surface, I'm using A3 watercolor paper with a quite fine texture

Here's a little more progress. I've desaturated the ocean to make the island stand out more, and added a graticule and finished the idea I had for the frame.
Click image for larger version. 

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