Price per square foot tends to goes down as square footage goes up.
(For example, a 1700 sq ft home in mountain view will cost you 2 mil. A 3400sq ft one in the same place will cost ~3 mil, not 4 mil).
If you wanted to buy a decrepit 600 sq. ft shack on a 10-acre lot in downtown Woodside, a price per square foot metric might seem like it should be <$1M. In reality the property would sell for $10M+ based on the land value, with the shack having negative value because of the cost to tear it down. (Ob. Steve Jobs Woodside reference here.)
I lobbied to put both on here, but then you end up with an unreadable map.