Apple Motion 5.1.1 - Manual (Page 215)

Chapter 7 Basic compositing 215
2 Do one of the following:
•
Drag a corner handle to resize the layer’s width and height at the same time. By default, you
can resize the width and height independently, by any amount.
•
Press Shift, then drag a corner handle to resize the layer while locking its width and height
together, maintaining the layer’s current aspect ratio.
67% resize factor