Bay Area residents without health insurance are clustered geographically in neighborhoods in West Oakland, Richmond, and San Francisco's Mission District.
The finding comes from this fascinating map made by Kevin Johnson, drawn from data collected by the 2012 American Community Survey on where people without either public or private coverage live. (The Affordable Care Act should start producing a more homogenous clustering, especially with the current March 31st deadline for the uninsured to sign up.)
In the Bay Area, the uninsured tend to be concentrated in poorer areas. In addition to Oakland, Richmond, and the Mission, the most prominent hot spots also include Hayward, cities along the Peninsula south of the San Francisco, and a few places in the North Bay. As Atlantic Cities points out, the map of the Bay Area "show[s] a clear rich/poor divide."
That's in contrast to some other cities that Johnson produced maps for, like the one for Boston, which reveals almost no residents without health insurance. (That's thanks to the health care reforms spearheaded by then-governor Mitt Romney.) Also in contrast to other cities, our uninsured population is fairly diffuse—compare our map to, for instance, those that of Dallas or Washington D.C., in which the uninsured are much more tightly clustered.