In San Francisco, that would be the entire S.East quarter of the city. Know as '3rd street' generally, the main street, it is very poor, very polluted , and very high crime. Also avoid, in SF, the 'tenderloin' neighborhood on both sides of Market street, from Union Square to City Hall, because of nighttime prostitution and drug dealing with gang shootings that recently have killed SF tourists, especially at night. Also avoid the west side of City Hall, the 'western addition' neighborhood, as it is mostly a poor , black, high crime area of children with guns taking iPhones away on the sidewalks! Stay "above / N. of Geary street" is a very good guideline. Japantown is relatively safe.
In San Jose,Ca. avoid the poorer, very high crime, many more Mexican gangs, entire 'Eastside', east of highway 101, especially at night! but even daytime !!
Always avoid Richmond, Ca. ,,, and the flats of downtown Oakland, Ca. due to insufficient policing, especially at night.
