San Jose, which is ostensibly a city, is only a little more dense than Nassau County, which isn't anything like a city. Manhattan is more than four times as dense as San Francisco. Although there are a bunch of geographical barriers preventing super-high population density in the Bay Area, there's still a lot of room for more people.

This is pretty misleading because San Jose's density is very uneven. There are large parts of the city that are completely uninhabited.

Interestingly, San Francisco is the second most densely populated large city in the US after New York. http://en.wikipedia.org/wiki/San_Francisco

Quite true, but density ratings can always be a bit tricky as they vary a lot by how much extra land cities have.

San Jose's 5,000 per square mile underestimates what it feels like to live there.

See the borders: https://maps.google.com/maps?q=San+Jose,+CA&hl=en&sl...

All that area in the southeast are farms and mountains. A The entire northern part are marshes. Its "effective" density is really much closer to 7-8,000 per square mile.

Los Angeles is also one where the density numbers underestimate the feeling of it. https://maps.google.com/maps?q=Los+Angeles,+CA&hl=en&...

A lot of that land is mountains. Indeed, south-central and central parts of LA have about the same population as SF and pretty much the same density: http://projects.latimes.com/mapping-la/neighborhoods/populat...

He's not - he's comparing them to two of the densest cities in the Bay Area (San Francisco and San Jose). The New York boroughs each have a bit less than half the land area of their Bay Area equivalents, but have much higher populations.

In fact, now that I'm reading up, the closest equivalent to a borough is a county of the Bay Area (each borough was originally a county, before the NYC consolidation of 1898).