From time to time the game will allow you to buy for a very cheap price a new piece of territory, where you can grow your city.

Before you buy new territory, you should inspect surrounding territories and pick the best one when you're buying. It should have both the resources you need and connection to the outside world.

It is a good idea not to buy a new territory immediately as it becomes available, unless you have already chosen a place to buy, because, for example, you need a water tank to build advanced wind turbine.