On the average weekday, San Francisco gains about 160,000 more bodies in the form of workers who commute in from various Bay Area counties, and counties even further to our north, south, and east. We learned that figure earlier this year via the American Community Survey, and it amounts to the difference in the number of people who commute in for work versus those who live here and commute outside of the city, like down the Peninsula, for work. We actually gain a total of 265,000 people each weekday, but lose 103,000 who reverse-commute out to the 'burbs. (The figure is based on data collected between 2006 and 2010, and given how much SF has changed economically in the last six years, and all of the awful traffic we now have, the daytime population has likely followed suit.)
Above we have a GIF above made by data geek Mark Evans, who used ACS data on commuters to create a series of these maps, including one here for Sacramento. Each color represents a county, with blue representing all far-flung counties together, the size of each dot represents the size of a cluster of commuters from that county. This map shows commuters from elsewhere who work in San Francisco County and who travel travel between 10 and 100 miles every day to work representing 87 different census tracts. As you can see there are a ton of people who drive in daily from northern Sonoma, south of San Jose, and as far east as the Delta and Tracy (their dots actually fly off the visible part of the map).
Below, we have the map depicting reverse commuters who live in SF and commute outside the city 10 to 100 miles every day. You can actually go here and select any county in the US to see visualizations based on this data trove.
Evans says he has an affinity for "new visualizations and data analytics techniques," and as he told LAist last month, he got interested in this project because he's a commuter himself.
"I've been astonished at the distances involved in many of these workers," he says. "I personally hate commuting and consider it a waste of 'life-time'. I'm sure people have good reasons, but I think they'd all be much happier if they lived close to work (or worked close to home)."