"… this notion of ‘depth’ is an elusive one
even for a mathematician who can recognize it…."

— G. H. Hardy,  A Mathematician's Apology

Part I:  An Inch Deep

IMAGE- Catch-phrase 'a mile wide and an inch deep' in mathematics education

Part II:  An Inch Wide

See a search for "square inch space" in this journal.

Diamond Theory version of 'The Square Inch Space' with yin-yang symbol for comparison

 

See also recent posts with the tag depth.