How do you unlock more land?

Some extra land can be unlocked around the edges of your city. This may depend on your level.

Look around the outsides of your walls for padlock icons. Tap these to unlock the areas, it will cost some resources to do so. You need to unlock the areas in specific order though so when you tap you may be told that you cannot unlock that one, Use the Go To option to take you to the next one you can unlock. There are level requirements so you may not be able to unlock any yet.

Click on the plots around your town with the padlocks and it will tell you the requirements per plot.