In terms of terrain maps, it's really just an issue of expanding cold/arctic regions during the winter. I can do it myself, but I'm unclear as to the difference between "cold" regions and "arctic" regions, and also on the overlap between either of these and "mountain" regions. The current texture image (map_earth_day.jpg) seems to have been taken sometime around March. There are clearly "mountain" regions that have snow on them, and the "cold" region overlaps both green and snow-covered areas.
I can just make it up as I go, but if there are actual conventions I'd rather follow them.
Also, if anyone is still having issues compiling from the latest posted patch, please let me know.