Sacramento, CA USGS
[unfortunately, in trying to update this, I accidentally wiped the title and description from it and it has been so long that I can’t remember any of the details. Let’s see how well I can wing it…]
I used a USGS topographical survey data to determine the height of the map, then meticulously edited in the water to flow in an acceptable way, finally topping it off with a proper scale of the highways and railways around Sacramento. I believe I used Google Earth on top of my local knowledge to sculpt the highways to feel as accurate as I could get to the state that they had existed when Cities:Skylines first launched.
The process was done over several versions.
Revisions:
Old revisions of this mod are available below. Click the link to download.