Very cool, the city is fantastic (though quite out-of-scale with the mountains )!

I think your lines could use some clean-up, you have double lines in a lot of places. If you choose to color it digitally, that kind of clean-up is easy to do in PS. If you go with watercolors (which I vote for, by the way!), you can do it by going over the lines with ink again, thickening them to hide the double. Some unevenness in line weight just adds interest. Unless you are going for a sketchy style, of course; then keep it

If you choose watercolors, make sure the ink is waterproof first. Even if it says waterproof on the pen, test it! I ruined a map once by assuming that the manufacturer didn't lie