The rule that decides what is registered
In the United States, an antenna structure must be registered with the FCC if it is taller than 200 feet above ground, or if it is near an airport and tall enough that the FAA must be notified. That registration, the Antenna Structure Registration (ASR), is where every public tower map, including ours, gets its list of towers. The rule exists for aircraft safety, not to catalogue cell service, which is why it misses a lot.
A 150-foot monopole in a suburb, well away from any runway, usually needs no ASR. Neither does an antenna on a rooftop that does not raise the building's height enough to matter to aviation. Millions of people are served from sites like these.
What is usually missing
- Small cells on streetlights and utility poles, including almost all millimetre-wave 5G.
- Rooftop sites on apartment blocks, offices and hotels.
- Shorter monopoles and stealth sites (monopines, flagpoles, steeples) away from airports.
- Indoor systems in malls, stadiums, hospitals and offices, known as distributed antenna systems.
- Water tanks with antennas, unless they are tall enough or near an airport.
How we fill part of the gap
On top of registered towers, our tower finder adds sites listed on 850 MHz cellular licences, which name each transmitter's location whether or not the structure is registered. These show as "Cellular licence site". They cover mainly AT&T and Verizon, which hold most of those licences, and they fill in some shorter sites in the areas those licences cover.
Newer spectrum, including the bands used for most 5G, is licensed by area with no list of sites, so the gap cannot be closed from FCC data alone.
What registered towers also include
The registry is not only cell towers. It includes TV and FM broadcast masts, public-safety radio towers, utility and railroad communication towers, and tall buildings registered because of their height. Our results show the structure type and owner for each, so a 1,000-foot guyed mast owned by a broadcaster is easy to tell from a carrier monopole. We exclude AM radio arrays, which are clusters of broadcast masts that do not carry cell service.
Spotting an unlisted site
If your phone shows strong signal and nothing registered is close, look around: a rooftop with rectangular panels at the edges, a streetlight with a box near the top, or a tall "pine tree" that does not match the others. Crowdsourced signal-mapping projects, where volunteers log cells as they travel, often show these sites too.
Other reasons a tower is missing or out of date
- Newly built towers appear once the owner files the construction notice with the FCC; our data refreshes monthly.
- Towers that have been taken down are removed once the owner reports it. We only list structures marked as constructed and not dismantled.
- Coordinates come from the owner's filing and are usually accurate to within a few metres, but older filings are sometimes off by more.