Boston would be a great addition to the game. Rivers and harbors separate the city, and it the city has a vivid color scheme for its rapid transit system (orange, red, blue, green). You could also draw colors from the bus and commuter rails (silver and purple).
We get many awesome city suggestions and we’ve seen Boston a few times. Check out the City Suggestions thread and you can add your voice there: http://community.dinopoloclub.com/t/city-suggestions/