I dislike how bold the color of the lakes is compared with the color of the oceans. I would either make them a closer color or the same color altogether. They just stand out a bit too much to me.

Why'd you make the resolution so much smaller here? It's what, 1/10th the size of the actual picture you work with? Just curious.

RPMiller makes a great point. Try and figure out some of the weather patterns, like currents and hurricane spots and, I would recommend, any plate tectonics you can. Unless they're Japanese, people won't be living in high-earthquake and high-volcanic activity areas. That island up to the north that's largely mountainous, for example, would likely not have any huge cities in it. Small mining towns and fishing villages I think would actually be in abundance, but there will be no agriculture and the terrain should be unstable, which would make the land one where people would not group together in large cities.