Tower structure types explained

The federal register records a structure type for nearly every registration. It is a short code, and it is more informative than it looks: the type usually tells you when the site was built, what it was built for, and how much the person building it was willing to spend.

The big three, plus two

Five codes cover ninety per cent of everything constructed.

Lattice tower

An open framework of steel members, usually triangular or square in cross-section. Lattice is structurally efficient — it carries heavy loads with relatively little material, and it presents a small surface to the wind, which matters more than you would think.

Lattice is the classic choice for broadcast and for multi-tenant wireless sites, because it can carry a lot of equipment. It is also the least popular with planning authorities, which is a large part of why it is less common in new urban construction.

Monopole

A single tubular shaft, usually tapered, often with antennas mounted flush or on short arms.

Monopoles carry less than lattice for the same height and cost more per metre. They are chosen anyway, constantly, because they take almost no ground space and read as far less industrial. In built-up areas the deciding factor is usually the planning application rather than the engineering, and a monopole is much easier to get approved.

Guyed tower

A slender mast held upright by tensioned cables anchored in a ring around it, typically at a radius of about 60–80% of the mast height.

This is by far the cheapest way to go very tall, which is why nearly everything above 300 metres in the United States is guyed. The catch is land: the guy anchors need a large clear area, which rules guyed towers out anywhere with expensive real estate. They are a rural form.

Almost every one of the tallest structures in the country is a guyed mast on cheap flat farmland, usually carrying television transmitters.

Pole and Tower (unspecified)

Two catch-all codes. TOWER is the single most common entry in the whole file — a freestanding tower whose construction the registrant did not further specify. POLE is the same idea at smaller scale. Neither tells you much beyond the height, which is a limitation of the data rather than of the structures.

Mounted on something else

A large group of registrations are not purpose-built at all. They record antennas attached to structures that exist for another reason.

Building with antenna is the most common of these: antennas on an existing rooftop. In dense cities this is a substantial share of registered infrastructure, and it is why the tallest “structure” in a downtown area is often a skyscraper with a mast on top rather than a tower.

Tank is a water tower or storage tank. Municipal water towers are ideal antenna sites — they are already the tallest thing around, they are already owned by the local authority, and the lease income is welcome. If your town has a water tower, it very likely has antennas.

Smokestack, silo and bridge appear for the same reason: something tall already exists.

Utility pole covers antennas on existing distribution poles, which is where much recent small-cell deployment has gone — though most small cells are below the registration threshold and never appear in this data at all.

Camouflage

The register has a TREE code, and it means what you fear: a structure disguised as a tree.

These are common in areas with strict planning rules, and they are rarely convincing at close range. The registration records the disguise honestly, which is a small piece of transparency the industry does not always volunteer elsewhere.

Arrays

A family of codes — 2TA1, 3TA2, 4GTA3 and so on — denote one element of a multi-tower array. 3TA2 is the second tower of a three-tower array; the G variants are guyed.

Almost all of these are AM broadcast. AM antennas radiate from the entire tower structure rather than from something mounted on it, and multiple towers fed with carefully controlled phase differences will shape the signal into a directional pattern — typically to protect another station on the same frequency, or to concentrate coverage over a population centre rather than over empty land.

If you see three or four registrations at nearly identical coordinates, with consecutive numbers and identical heights, you are looking at an AM array. It is one of the more visually distinctive things in the data.

The oddities

The long tail includes oil and gas rigs, billboards, and a handful of categories that appear a dozen times nationally. There are 174 distinct structure types in current use. This site names the ones it can name confidently, and where it cannot, it shows the raw code and says so rather than inventing an expansion.

What you can infer from type alone

• Guyed and very tall → almost certainly broadcast, almost certainly rural
• Monopole → probably wireless, probably built in the last twenty-five years, probably in a place with planning constraints
• Lattice, moderate height → probably a multi-tenant wireless site
• Building with antenna → urban, and the height figure is telling you about the building
• Tank → municipal, and there is a good chance the local authority is the landlord
• Tower array → AM radio