Hardest place to find empty housing? California!

Looking for housing in California — to buy or rent — means having the fewest choices in the nation.
A curious stat from the U.S. Census Bureau tracks empty residences, whether those units are rentals or ownership properties. Basically, “gross vacancy rate” is a proportional measure of how many places are available in a geographic area.
When I put this housing-supply data into my trusty spreadsheet, I found California has had nation’s lowest vacancy rate in five out