I selected this image that I scanned from a TMNT comic to represent what I understand as scale.  The top box of this comic is a perfect representation as the villain is scaled very large to give off the affect that he is much closer to us, and the opposite for Raphael, Leonardo, Michelangelo, and Donatello as they are scaled way down to appear farther back in the distance from us.  This strategy is the most popular aspect of scale as every cartoonist / graphic novelist scales to give depth or distance between objects.  A great example of this in the real world is those photos people take where someone who is very close to the camera appears to be holding a person in their hand while in reality the person is just perfectly aligned and very far back from the other person.  There are a lot of visual tricks that can be pulled of with scale that imply depth.  I would also say that it is subjective depending on the persons interest, if its a photo of me with a volcano in the background I may scale myself up so I look comparative or as important as the backdrop of the photo.