But They Made New York Great. (Sometimes.)

New York City’s zoning code turns 100 this year. That may not sound like cause for celebration — except maybe for land-use lawyers and Robert Moses aficionados. Yet for almost every New Yorker, the zoning code plays an outsize role in daily life, shaping virtually every inch of the city.

Whole swaths of the city defy current zoning rules. In Manhattan alone, roughly two out of every five buildings are taller, bulkier, bigger or more crowded than current zoning allows, according to data compiled by Stephen Smith and Sandip Trivedi. They run Quantierra, a real estate firm that uses data to look for investment opportunities.

Mr. Smith and Mr. Trivedi evaluated public records on more than 43,000 buildings and discovered that about 17,000 of them, or 40 percent, do not conform to at least one part of the current zoning code. The reasons are varied. Some of the buildings have too much residential area, too much commercial space, too many dwelling units or too few parking spaces; some are simply too tall. These are buildings that could not be built today.

It is important to note that these estimates rely on public records that can be imperfect. Still, while the data may at times be imprecise, it allows for an insightful view of zoning in New York.