I actually saved versions of the progress of this map while working on it. I figured someone might enjoy seeing the steps of the progression in the image. The initial sketch was done very very quickly (probably in about 2 hours or less), but everything else sticks to this pretty closely. Total time for this creation was about 40 hours. The resolution was intense to work with (9000x5400). The single layer Photoshop file is 184mb.
I like to paint all on one layer. I just seem to be able to control light better this way and it keeps the file simple.