Hello Jennifer,
Thanks for your interest in Syncfusion products.
As with your queries,
All the drawing elements such as Rectangles if used to populate a diagram, then they are recognized as a diagram object or instances of the Diagram control.
If your intention is to retrieve the properties of the diagram object then , you can go with it by using the Diagram's utility methods and properties.
I have created a small sample implementing this which would help you modify the properties of the diagram objects including its size,height,name,etc.
Please do let us know if we can be of further assistance to you.
Regards,
Praveena.
DiagramObjects.zip