Arbitrary polygons are shapes with no external authority: nobody can look up "the" boundary the way a county line can be looked up in a TIGER file, because the boundary was drawn — by a human digitizing a delivery zone, by a drive-time model, by a customer-catchment algorithm — for a specific purpose and exists only in the system that drew it. This is the defining difference from administrative boundaries: there is no vintage to reconcile against, because there is no canonical version to reconcile with. The tradeoff is flexibility for verifiability — an arbitrary polygon can be regenerated at will, but nothing external confirms it is correct.
- Cardinality
- No partition guarantee — polygons may overlap or leave gaps by design
- Governed by
- Whoever drew or generated it — no external authority to check against
- Not a geometry
- A parcel APN or territory label — the shape lives in the polygon file, not the code
- Converts via
- Repair (self-intersection, holes) then polyfill under center/full/intersect/threshold
Members
| Member | What it is | Typical generation method |
|---|---|---|
| Trade area | A store's modeled customer catchment | Drive-time isochrone or gravity model |
| Delivery area | A courier or fulfillment service boundary | Manual digitization or routing-engine output |
| Geofence | A presence-targeting or measurement polygon | Manual digitization (KML/GeoJSON) |
| Venue campus | A stadium, mall, or airport footprint | Manual digitization from imagery |
| Store catchment | Observed or modeled visit-origin area | Visit-data clustering or isochrone |
| Parcel | A legal land boundary | Assessor / cadastre survey |
| Regulatory zone | A jurisdiction-drawn compliance area (e.g. emissions zone) | Regulatory-body digitization |
| Weather polygon | A storm warning or advisory area | Meteorological model output |
| Custom sales territory | An internally defined rep or region boundary | Manual assignment, often built from admin unions |
| Exclusion zone | An area explicitly carved out of a target set | Manual digitization or set subtraction |
Required metadata
| Field | Why it's required |
|---|---|
| Generation method | Determines how much to trust the boundary — a surveyed parcel and a hand-drawn geofence carry very different confidence |
| Vintage / generated-at timestamp | A trade area or catchment is a model output tied to the data it was fit on; it goes stale as conditions change, even with no external redraw event |
| CRS | Especially important for parcel data from assessors, which is frequently delivered in a state-plane or other projected CRS |
| Author / purpose | A geofence drawn for measurement and one drawn for targeting may look identical but license and privacy handling differ |
Common risks
Because nothing external validates an arbitrary polygon, geometric defects that a surveyed boundary would never contain show up routinely here: self-intersection (bowtie rings, most often from manual digitization or a model artifact, which make area and containment undefined until repaired — see geometry normalization); holes (an interior ring — a courtyard carved out of a campus polygon, a competitor's parcel excluded from a territory — that must be passed through to the filler intact, not silently filled over); narrow slivers and tiny polygons (a delivery area a few hundred meters wide, or a parcel smaller than a single cell at the working resolution, can legitimately produce zero center-contained cells, which is a correct result of the containment rule, not a bug); and simplification drift (a boundary run through Douglas-Peucker-style simplification for file-size reasons shifts vertices enough to change which cells qualify, especially at higher resolutions where cell edges are shorter than the simplification tolerance).
A parcel's assessor identifier (an APN) is worth flagging on its own: it identifies a legal record, and the polygon it's joined to may lag a subdivision, merge, or boundary adjustment recorded at the assessor but not yet reflected in the geometry file — the id and the shape can drift apart even within this family, in the same way an administrative id can outlive its boundary.
How it converts to H3
All ten members above share one conversion path: buffer or otherwise
normalize the polygon, then polyfill under center, full, intersect, or
threshold containment. See
arbitrary polygon to H3 for the full
containment-mode comparison and the repair steps for self-intersections and
holes. A shape that is described as a fixed radius around a point — "3 miles
around this store" — is not an arbitrary polygon even if a system stores it
as one; it belongs to
point-radius geometries, and forcing it
through this path discards the radius-units question that family forces
explicitly.