Riverview,Sunset Valley are the most common sim city worlds in Sims 3. Now with the Sims 3 Create a world tool, you can create your own world!
Getting the tool would be easy if you have a registered Sims 3 product, you can register your game at their official site : Sims 3
However, using the tool is not so easy as it seems. With the official tutorial you too may can create an awesome world for your sims to live in.
click here: Create a world Tutorial
Note: This tool is only available for PC users only.