What the tower database misses, and why your neighbourhood looks empty

The most common reaction to a site like this one is: there’s a tower two streets from me and it isn’t on here. Usually the site is working correctly and the tower genuinely is not in the federal register. This is the single most important thing to understand about the data, so it is worth setting out plainly.

What requires registration

The FCC requires registration of antenna structures that may affect air navigation. In practice the threshold is:

• Structures over 200 feet (about 61 metres) above ground, anywhere; and
• Shorter structures near an airport, where the required height falls off on a sliding scale with proximity to a runway

That is the whole test. It is an aviation rule that happens to produce a communications dataset, and its coverage reflects aviation concerns rather than what a curious member of the public would want to know.

What is therefore absent

Small cells. The bulk of recent capacity growth in cities has gone into equipment mounted on utility poles, streetlights and building faces, typically 6–12 metres up. None of it needs registration. None of it appears.

Rooftop installations. Antennas on an existing building generally do not require their own registration unless the combined height crosses the threshold. A great deal of urban coverage comes from rooftops that are invisible in this data.

Short masts. A 40-metre tower away from an airport does not register. Rural wireless internet providers use a lot of these.

Indoor systems. Distributed antenna systems in stadiums, airports, shopping centres and office towers are substantial pieces of infrastructure and are entirely outside this dataset.

Anything unlicensed or low-power. Wi-Fi, private LTE, and similar.

Why the gap is growing

Networks have densified. Fifteen years ago, adding capacity meant building another tall tower. Today it usually means adding many small radios close to the ground, because the frequency bands being deployed do not travel far anyway.

The registration threshold has not moved. So the share of real infrastructure captured by the register keeps falling, particularly in cities, and particularly for the newest deployments. The register is an increasingly good record of tall structures and an increasingly partial record of mobile coverage.

What the data is genuinely good for

Given all that, what remains?

Tall structures, comprehensively. If it is over 200 feet, it is here. Broadcast masts, major wireless towers, water tanks, industrial stacks. For anyone interested in the tall built environment, this is an excellent dataset.

Rural coverage infrastructure. Where a single site has to cover a wide area, it has to be tall, and tall means registered. Rural coverage is far better represented than urban.

Ownership patterns. The register shows who owns American vertical infrastructure at national scale, which is not visible anywhere else in one place.

Historical build-out. Construction dates go back decades, so the data shows when different regions built what.

Density comparison between places. This is what our city and state pages are for. The absolute numbers understate reality everywhere, but they understate it in a roughly consistent way, so comparisons between places remain meaningful.

A worked example

Take a dense city neighbourhood. The register might show three registered structures within two kilometres: a rooftop installation on a tall office block, a lattice tower in an industrial strip, and a water tank.

Actual coverage equipment serving that same area might include those three plus forty small cells on streetlights, a dozen rooftop sites below the threshold, and a distributed antenna system in the shopping centre. The register shows you three of perhaps fifty-five installations.

Now take a rural county. The register might show eight structures. Actual coverage equipment might be those eight, plus a handful of short masts. The register shows you eight of perhaps twelve.

Same dataset, very different completeness. That is worth keeping in mind whenever you compare a city page to a rural one.

How we handle it

Every list page on this site carries a note about coverage, and we describe entries as “registered structures” rather than “cell towers” wherever the distinction matters — because a large share of them are not cell towers, and a large share of cell towers are not in here.

It is less catchy. It is also true.