Cell phone data reveals which California counties are not socially distancing

A man crosses a nearly empty street in San Francisco, Tuesday, March 17, 2020. A man crosses a nearly empty street in San Francisco, Tuesday, March 17, 2020. Photo: Jeff Chiu/AP Photo: Jeff Chiu/AP Image 1 of / 49 Caption Close Cell phone data reveals which California counties are not socially distancing 1 / 49 Back to Gallery

Want to know which California counties are evidently not doing a very good job of obeying the statewide shelter-in-place order that has been in effect for over a week now?

The data company Unacast, a firm that collects cell phone location data for private companies, created an interactive map that shows which counties in California and beyond are correctly "socially distancing" by staying at home.

Each county and state is graded on an A-F basis on the "change in average mobility," or the decline in distance traveled since quarantine measures were first put in place.

"To calculate the actual underlying social indexing score we combine tens of millions of anonymous mobile phones and their interactions with each other each day - and then extrapolate the results to the population level," Unacast writes in its methodology.

While it is somewhat unnerving to know we're being unwittingly tracked at all times, the data is useful in providing a picture of social distancing at work.

The state of California received an "A" grade overall thanks to a 40 percent decline in average distanced traveled, but several counties — all in rural areas with few reported cases — have actually logged an increase in distance traveled since the shelter-in-place order was issued. However, this could be partially explained by the fact that residents of these counties have to drive further to reach grocery stores, restaurants for takeout and other essential services.

Every Bay Area county with the exception of Solano County received an "A" grade, and the region's numbers for reductions in average distance traveled is in line with other national hot spots including New York City and New Orleans. Here are the nine Bay Area counties ranked in order of "best at social distancing" to worst:

1. San Francisco County: 65 percent decrease (A)

2. San Mateo County: 63 percent decrease (A)

3. Santa Clara County: 61 percent decrease (A)

4. Marin County: 56 percent decrease (A)

5. Napa County: 54 percent decrease (A)

6. Alameda County 51 percent decrease (A)

7. Contra Costa County: 48 percent decrease (A)

8. Sonoma County: 41 percent decrease (A)

9. Solano County: 37 percent decrease (B)

You can play with the interactive map above. It is somewhat buggy, but refreshing the page usually does the trick. Click here to access the original version.

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Eric Ting is an SFGATE digital reporter. Email: eric.ting@sfgate.com | Twitter:@_ericting