This page exists to state, as directly as possible, the rule the rest of this catalogue keeps returning to: an identifier is not a geometry. Every other family in this catalogue is a shape, or a rule for constructing one. This family is a label — a string or code that some system uses to refer to a geographic region — and the region it refers to is not encoded in the label at all. It is encoded in a boundary file, at a specific vintage, resolved through a specific crosswalk. Two systems can hold the identical identifier and disagree completely about what territory it covers, because the label never changes even when the boundary underneath it does.
- Cardinality
- A label, not a shape — one id per region per namespace
- Governed by
- Whichever platform or standard minted the id (FIPS, ISO, DMA, publisher)
- Not a geometry
- The id itself — the recurring warning this whole page exists to state
- Converts via
- No direct conversion; H3 resolves outward through a maintained, versioned crosswalk
Members
| Member | What it is | Typical namespace |
|---|---|---|
| Postal id | A postal-service delivery-area code | ZIP, ZCTA, national postcode |
| FIPS code | US Census/federal region code | FIPS state/county code |
| ISO code | International country/subdivision code | ISO 3166-1/2 |
| DMA id | Nielsen media-market code | DMA code |
| Publisher id | A media owner's own market label | Publisher-internal |
| Internal market identifier | A company's own named region | Internal, often undocumented outside the owning team |
Required metadata
| Field | Why it's required |
|---|---|
| Id namespace | The same string can mean different things in different systems — a bare "501" is meaningless without knowing which namespace produced it |
| Boundary vintage | The version of the boundary set the id was minted against — this is what actually determines the geometry, not the id itself |
| Crosswalk source | The specific mapping table or service used to resolve the id to a boundary, since two crosswalks built from different vintages will disagree |
Common risks
Resolving a platform identifier to a geometry requires exactly three things: the namespace it belongs to, the vintage of the boundary set it was minted against, and a crosswalk that performs that specific resolution. Skip any one of the three and the "geometry" produced is a guess, not a lookup — this is true even when the id itself never changes, because the boundary underneath it can move without the id being reissued.
Namespace ambiguity is the most common failure: two vendors' "market
12" are different regions, and nothing about the string "12" signals
which vendor's scheme is in force — ingesting an id without recording its
source namespace makes it silently ambiguous the moment a second data
source enters the pipeline. Vintage mismatch compounds this: even
within one namespace, an id assigned against a 2019 boundary set and
resolved against a 2024 crosswalk can resolve to a different polygon,
because DMA and postal boundaries specifically are redrawn on cycles far
shorter than most systems' assumed "this never changes" treatment of a
region code. Unmatched ids dropping silently is the operational
failure mode: a join between an id-keyed dataset and a crosswalk table
that fails to match — because of a vintage gap, a namespace collision, or a
simple typo — commonly drops the unmatched rows rather than raising an
error, which understates whatever metric is being computed with no visible
signal that anything went wrong. Platform-native-ids-only constraints
are related but distinct: some platforms accept no polygon or coordinate
input at all and require everything expressed as one of their own ids,
making a versioned crosswalk to that namespace the only way in — one that
must be maintained continuously as the platform revises its boundary
definitions, on its own schedule, invisible to the caller
unless the platform documents it.
How it converts to H3
Because a platform identifier is a reference rather than a shape, there is no direct id-to-H3 polyfill — the conversion runs in the opposite direction, from H3 to the platform's id space, through a maintained crosswalk. See H3 to platform-native geography for how the crosswalk is built and versioned, how unmatched cells are reported rather than dropped, and how precision loss is quantified when a platform's id granularity is coarser than the H3 resolution expressed. Where the underlying region is available as an actual polygon, treat it as an administrative boundary instead and skip id resolution entirely — the polygon is strictly more information than any id that merely points at it.