BBL vs. BIN: the NYC property identifiers researchers should not mix up

BBL identifies the tax lot

A BBL combines borough, tax block, and tax lot. It is the natural key for tax-lot, PLUTO, zoning, assessment, and many finance records. The formatted pieces matter because leading zeroes are significant when constructing the canonical ten-digit value.

BIN identifies the building

DOB assigns a BIN to a building. Permit, job, violation, and certificate records often match most reliably by BIN. A tax lot can contain multiple buildings and therefore multiple BINs.

Condominiums need extra care

A condominium can have billing lots for individual units plus a shared building or base-lot context. A unit's tax-lot records and the building's DOB records answer different questions. Preserve the mapping instead of collapsing every lot into one identifier.

• Use BBL for parcel and tax-lot records.
• Use BIN for building-system records when the source supports it.
• Record fallback matching by address, block/lot, or radius explicitly.

Why identifier provenance matters

When two records appear inconsistent, first ask whether they refer to the same lot, the same building, and the same time period. LotContext records the resolved identifiers and source match method so a reviewer can retrace that decision.