Quick reply to Korash- Way too long! Days, certainly, but I'm not sure how many. I agonize over very small details.
jfrazierjr- I'm not sure I followed your instructions very well. I did manage to select the area between the paper and the image limits, but could not find 'delete' option anywhere. I tried cutting, to no avail. So I just started looking through the options I did have. At one point I could see the checkerboard behind the paper (though I'm not sure how I did it), but I could still see the parts of the map that ran past the paper's edge under the checkers, so I figured that wasn't it. In the end I filled the selection with white. I then saved it as a .png file. I'm not sure how big it was before this save, but the current image is 6.94 MB. I reduced the image by 50% so that I could post the result.
This is the flat white jpg I'm coloring, also reduced
Stern's Bridge coloredit2 reduced 50%.JPG
Here is the result of jfrazierjr's instructions, as well as I could follow them
Stern's Bridge coloredit3.PNG
Final note, I am again filled with uncertainty. Is this the direction I wish to be going? It seems... I don't know, wrong, but I don't know why. Should the coloring stop? Should the hues change? I will continue coloring for now, because I don't have any better ideas, and I know that on completion they are easily restored to white or altered to another hue.