Final answer:
Vitruvius's theory focused on ideal proportions in buildings and the human body, while Leonardo da Vinci's drawing depicted the ideal human proportions based on that theory.
Step-by-step explanation:
The difference between Vitruvius's theory and Leonardo da Vinci's drawing is that Vitruvius's theory, as described in his book 'On Architecture,' focused on the ideal proportions of buildings and the human body, while Leonardo da Vinci's drawing, known as the Vitruvian Man, specifically depicted the ideal human proportions based on Vitruvius's theory.