Social City has just released an enormous feature today - the ability to add huge expansions to your city through Districts. Districts are whole new city additions that you can add on to your city. They have their own happiness and population, and basically work similar to how multiple islands work in Tiki Resort or Happy Island. Districts are only available to players level 12 and up, and can be accessed with the new "Map" button in the upper right corner of your city.
Currently, only one additional district is available, and it's located Southeast of your main district and costs 100,000 coins to unlock. Additional districts will be unlocking in the future, but they may have special requirements and prices to access them. When you click on a neighbor to visit their city, you will now be taken to their overhead map and given the option to visit each district individually. Players so far a bit upset that these districts act as separate entities entirely and are not directly 'linked' to the main district.
Have you expanded your city yet to the Southeast? What do you think of this new feature?