I didn't post it as a WIP as I thought that it was finished. Clearly, based on the responses, that's not the case. Don't get me wrong, I appreciate the feedback and plan to act on all the good suggestions. Is it possible to move this thread to "Region/World Mapping" section as a WIP? (I assume a moderator or admin will need to do this.)
I would, however, like to comment on the observation that Elterio Delgard made regarding the rivers.
Realistically, at the scale of my map, rivers shouldn't even be visible. For example, here's a shot of the Grand Canyon (clipped from Google Earth), at an altitude much much lower than that of my map:
Attachment 84388
As you can see, while Lake Powell and Lake Mead are visible, as is the canyon itself, the Colorado River is too small to be seen.
Regarding the missing vegetation along the sections of river passing through desert regions, this would be a problem
if those regions were being irrigated and crops were being grown. However, if no human activity is present, there's no reason why substantial plant life should be visible at the given altitude. Here, for example, is an image (again from Google Earth) of the present-day Upper Nile:
Attachment 84389
This is at roughly the same altitude as the Grand Canyon image (above). Note that while broad areas of vegetation are visible in some locations, much of the land immediately adjacent the river is barren. Given that areas of my map that show rivers through desert regions are unpopulated, I designed them to appear the same.