In order to position the shapes in the ViewPort and somehow center them within these bounds you can try using the Diagram.AutoFit command
or AutoFit() public method. As for the background Image, if it is in Canvas, you can set Canvas.Left , Canvas.Top to position it. On the other hand, since you know the Diagram.Viewport's size you can also set Width and Height on the Image. I hope this helps you move forward.
Check out Telerik Analytics, the service which allows developers to discover app usage patterns, analyze user data, log exceptions, solve problems and profile application performance at run time. Watch the videos
and start improving your app based on facts, not hunches.