The most interesting data in this fascinating compilation of statistics on San Francisco is the employment chart. Now: It's 2010 census data, which means it's out of date since this city has been changing radically in the past couple of years. But still: the largest number of jobs in this city -- by far -- falls into two categories, neither of which is tech. It's government (55,000) and health care/social services (89,000). Together, they account for 144,000 jobs. That's one third of all employment in San Francisco.

And Mayor Lee has not, to my knowledge, ever talked about either sector as worthy of the sort of attention he pays to companies like Twitter.

The reason this is so important: Most of the jobs in those sectors are decidedly middle-income. Yeah, a few government workers (high-ranking cops and firefighters, public-health doctors, a few department heads) make a lot of money. But most earn less than the amount needed to rent the median apartment in San Francisco, and a lot less than the amount needed to buy the median house. And that's the better-paid class.

Health care and social services workers (again, with the exception of doctors and agency directors) are typically paid even less than government workers.

Which means it's impossible for a third of the city's workforce to live in the city.

The only ones who live here are the ones who moved here long enough ago to find an affordable apartment -- and are protected (for the moment) by rent control, or those who bought houses more than a decade ago.

A statistic that isn't in the mix: How long the typical resident has lived here. The old adage holds that  a third of the city turns over every ten years, and while that's probably an overstatement, it's clear that significant numbers of workers in every sector have been here for a short enough time that they're facing an impossible housing situation.

At our forum last week on Plan Bay Area, Mike Casey, the head of Local 2, the hotel workers union, lamented that so many of his people now live far out of town that it's hard to put together a picket line or rally: After work, the union members head home to Brentwood or Antioch, and they're not coming back an hour later for a protest.

Why isn't this the biggest priority at City Hall?