You can practically call your namespace anything you want. Different languages seem to have their own conventions, but the reverse DNS style is what I like the most.
Your DNS is unique to you, so it is a great idea to create your namespace using it.
If my domain is
www.betweenthebraces.com you drop the www and flip the domain name to create your namespace.
My namespace is
From this point you can add your project name and any other packages you need.
com.betweenthebraces.myapp.Viewport might be the location of my main class for a mobile application.