That's like defining "New York City" as the five boroughs plus all of New Jersey, West Virginia, and central Pennsylvania. It's a meaningless mishmash of a definition.
Santa Clara county encompasses most of Silicon Valley "proper."
San Mateo county includes the peninsula which starts at Menlo Park and just NW of Palo Alto/Stanford.
It's hard to define clear boundaries of what San Jose because it sub/urban sprawls into many other communities (Campbell, Los Gatos, Cupertino, Santa Clara), like individual trees growing into one massive tree cluster. Plus, most readers out of the area aren't familiar where Willow Glen, Blossom Valley or Almaden Valley are without maps.
It might've been more interesting to compare the price fluctuations as a heatmap and a function of distance from economic intensive areas.
Right, but San Mateo County is omitted from their list, while San Benito and Monterey are included. It's nuts.
(San Mateo County begins at East Palo Alto and Menlo Park.)