Here is my current outline for Trident City, the setting of the fantasy/superhero setting I am writing. The city is based at the fork of a major river, near the borders of three nations. The city originally began as a collection of close fishing communities. As river travel and trade grew, it quickly expanded, becoming three close cities across the river and it's forks, and then into one metropolis. The territory belonged to one of the nations, but it was left largely alone and unoccupied, due to tensions between the nations and not wanting to appear as if they were militarizing the river region. Eventually, Trident City grew too big to be ignored and the nation tried to formally take it over for its economic and strategic value. The city, along with the other two neighboring nations, who wanted the city to remain neutral and indepedent for the sake of trade and keeping the staus quo. They were able to stave off the assault after a year-long siege. It's been 80 years since the war ended and the city has continued to build up and the districts have developed their own character. A number of districts were shaped by the war and continue to exist influenced by the past events. Each district has its own overall economic station and a few are very specialized.
Shieldhaven, for example, is made up of the military barracks along the east wall, where the siege took place, as well as residential areas that survived the siege. The Borricks are a huge slum area. Formerly called the Barricks, it was a district that served as a home for refugees from outside the walls and citizens from the eastern part of the city during the war. After the war ended, many had to home to go back to and no money to rebuild and so they stayed. They city has yet to build up the resources to demolish and rebuild the entire district, and so it remains a labyrinthine district of crime and squalor. Bruston, derived from its former nickname of Brutestown, is the western barracks district and where the soldires assigned to regulate the Barracks during the war were stationed. Pitchbrune is the industrial area, containing ore refineries and large-scale smithing operations. And so on.
I am still thinking of adjusting the district sizes. I reduced a few already that seemed too big for what they were and others have grown in the process. Crenton, for example, seems too large now and I'm considering splitting it into two smaller districts.