San Francisco, CA Night Sky Brightness (Reading Flagged)
San Francisco's reading looks wrong, and this site says so rather than hide it
San Francisco's satellite reading came back at exactly zero, which is not a real measurement for a city of 827,526 people, it means the sample point most likely missed the lit part of town, landing on open water, a shadowed hillside, or just a bad coordinate. Real cities this size do not read true zero.
This is flagged instead of shown as a normal result because reporting it as "San Francisco's dark sky" would be reporting a data error as a fact, see the data quality guide for how this gets checked.
The nearest reliable reading to San Francisco
Mill Valley, CA is about 30 miles from San Francisco and has a trustworthy reading: rural band. It's the closest usable stand-in until San Francisco's own figure is corrected.
Because San Francisco's own coordinate is what produced the bad reading, that distance figure is itself approximate, not a confirmed measurement.
San Francisco against the rest of the dataset
San Francisco, CA has a population of about 827,526, one of 3,206 US cities in this dataset, 3,187 of which have a usable brightness reading today.
The dataset and sampling method behind every one of those readings, flagged or not, are in the methodology guide.