Carriers' own coverage maps are drawn by the carriers, each in its own way. Since 2022 the FCC has required every mobile carrier to file coverage in one common format twice a year, and publishes the result as the National Broadband Map. It is the most consistent way to compare carriers, as long as you know what it measures.
Two maps per carrier: outdoors and in a car
Each carrier files where a phone gets service standing still outdoors, and separately where it gets service in a moving vehicle. The in-car map is always smaller. Neither covers indoor signal, which depends on the building.
4G LTE and two 5G speed tiers
4G LTE is filed at a minimum of 5 Mbps down and 1 Mbps up. 5G is filed at two tiers: 7/1 Mbps and 35/3 Mbps. A place can have 5G at the lower tier and not the higher one.
Filed by the carriers, open to challenge
The maps are the carriers' own claims. The FCC lets the public and governments challenge them with speed-test evidence, but the maps are not drive tests. Treat them as each carrier's best case, and check your own address.
Area, not people
NetScanAI's percentages are shares of area, as the FCC publishes them. A county can be 60% covered by area and still have every home covered, if nobody lives in the uncovered hills. For a single address, use the carrier's own map or the FCC map's location search.