Light pollution maps typically use satellite data from NOAA’s VIIRS to visualize levels of light pollution around the world. Some maps, like Light Pollution Map, also allow users to click on different locations to view detailed information - such as light pollution levels using the Bortle Dark Sky Scale.
My favorite dark sky map is actually the (identically named) Light Pollution Map. I like this map because it explains light pollution levels in clear, easily understood layman's terms. For example, where I live, the map tells me that the: “Entire sky is brightened. No Milky Way visible; only the brightest constellations can be recognized.” The Light Pollution Map not only displays the Bortle Scale for any location, but also does a great job of describing what you can realistically expect to see in the night sky.
Both maps use satellite data from NOAA’s VIIRS (Visible Infrared Imaging Radiometer Suite). VIIRS is a sensor aboard weather satellites that captures low-light imagery of the Earth at night. It’s one of the most reliable tools for measuring artificial light emissions globally and is widely used in scientific studies of light pollution.