3,206 cities, not every place
This dataset covers 3,206 incorporated US cities with a 2025 population of 10,000 or more, the same scope the Census Bureau's own population estimates use. Unincorporated communities, national and state parks, and rural land outside any city boundary are not in it at all, so "the darkest place in this dataset" is not the same claim as "the darkest place in the country." True wilderness darkness, the kind an actual DarkSky-designated park reaches, is darker than anything a city-only dataset can show.
"Nearest darker sky" is straight-line, not driving distance
Every city page names the closest other city in this dataset with a meaningfully darker brightness band, and the distance shown is calculated as the crow flies between the two sets of coordinates, not a road route. Real driving distance depends on the specific roads available and will always be equal to or longer than the figure shown.
A single annual composite, not a live reading
The underlying VIIRS composite averages many cloud-free nights across all of 2025 into one annual figure per location. It smooths out one-off events, a stadium's lights left on, a wildfire glow, a temporary construction site, which is the right choice for a stable year-round estimate but means this site cannot show what any single specific night looked like.
19 cities with a flagged reading, San Francisco among them
19 of the 3,206 cities here came back with a satellite reading of exactly 0.0, a number no real city this size actually produces, San Francisco (population 827,526) is the largest example. This almost always means the sample point landed off-target, water, unlit terrain, or a coordinate error, rather than a genuinely dark sky, so those pages say so directly and point to the nearest city with a usable reading instead of reporting the zero as fact.
Reporting an error
If a specific city's figure looks obviously wrong against what you've actually observed there, the contact page is the way to flag it; corrections are checked against the source VIIRS data directly, not changed on request alone.
Where to go next
See the range this plays out across: Truckee, CA, Roswell, NM, Oklahoma City, OK.
How DarkSkyCheck Measures Your City's Night Sky · The Bortle Scale, and Why This Site Doesn't Report One