What is actually being done to the building?

The commonest kind of work there is: 217,350 filings across the city carry a plumbing flag, from a replaced riser to a whole new system.

The broadest category on a filing: interior and envelope work that is not separately flagged.

The scaffold tunnel over the pavement — the most visible building work in New York, and the one New Yorkers ask about most.

Heating, ventilation and cooling — the plant that makes a building habitable, and the work most often filed alongside a conversion.

Work that touches the frame a building stands on — the filings most likely to change what a building can carry.

Work platforms up the side of a building, filed separately from the shed at its foot.

The boarding that goes up around a site before anything else does, and the fences that stay when it comes down.

Automatic fire suppression, filed on its own track because the city inspects it on its own track.

Illuminated and structural signage, which the city permits as building work rather than as advertising.

Excavation and site work — usually the first visible sign that something is coming.

Footings, underpinning and the work that happens before a building goes up.

A driveway across the pavement. Small work, and the permission a garage or loading bay depends on.

The dry and wet pipes a fire department connects its hoses to, required in most buildings above a certain height.

Filings that record photovoltaic work on a roof or facade, anywhere in the five boroughs.

Rooftop telecommunications equipment, filed as structural work on the building that carries it.