NASA had a workshop on that topic in 2015, the "TRANSFORMATIVE VERTICAL FLIGHT WORKSHOP" [1].

They were specifically asking: "Why is the Silicon Valley a great Early Adopter Market for civil VTOL?" [2] (Spoiler alert: getting from A to B on the road takes too long due to traffic...)

And yes, that study imagines 200 helipads scattered throughout the Bay Area.

[1] http://nari.arc.nasa.gov/tvf [2] http://nari.arc.nasa.gov/sites/default/files/attachments/Ant...