Advertising Geographic Matching Semantics

Geometry alone does not define who gets targeted; the matching semantic, location source, and lookback window determine the audience as much as the shape does.

The geometry is not the target

Two platforms can be handed the identical polygon — the same vertices, the same CRS, the same H3 cell set — and deliver to materially different audiences. This is not a bug in one of the platforms; it is because a targeting request is not fully specified by its geometry. It is specified by a GeographicTarget: geometry plus a matching semantic, a lookback window, a location source, a confidence level, and whether the geometry includes or excludes.

geometry: The shape itself — a polygon, circle, or H3 cell set. Necessary but not sufficient.
matchingSemantic: How a device or person is associated with the shape. See the seven values below.
lookbackWindow: How far back a presence event still counts as a match, e.g. 30 days, 90 days, or none (real time only).
locationSource: GPS, IP, publisher-declared, cell tower, or a probabilistic model. Determines the effective precision, independent of the geometry's own precision.
confidence: A score in 0 to 1 the platform assigns to a given location observation; low-confidence observations may be silently dropped or silently included.
inclusionOrExclusion: Whether the shape adds or removes eligibility. An excluded shape with weak matching leaks eligible devices back in.

The seven matching semantics

physical_presence: The device was observed inside the geometry during the campaign's active window. Requires a real-time or near-real-time location ping.
recent_presence: The device was observed inside the geometry within the lookback window, not necessarily during the active campaign. A 500m geofence with a 30-day lookback matches people no longer there.
home_location: The device's inferred home is inside the geometry, from a separate home-location model (typically overnight ping clustering), independent of any daytime movement.
work_location: Same as home_location but for an inferred workplace cluster, typically daytime-weekday pings.
interest: No location observation at all — the match is behavioral or declared (e.g. a user follows a page tagged to that region). The geometry is a proxy, not a location event.
presence_or_interest: A platform-defined union of a presence signal and an interest signal, most common on walled-garden platforms that blend both to maximize match rate.
platform_defined: The platform does not disclose which of the above it uses, or uses an internal blend that varies by inventory source. Treat as unknown precision until proven otherwise.

Same geometry, different audience

A DSP set to physical_presence with a 0-day lookback and a social platform set to presence_or_interest with a 30-day lookback, both targeting the same circle, are not comparable line items. One counts people who were there today; the other counts anyone who was there in the last month plus anyone who merely expressed interest in the area. Reporting them under one "targeted audience" number is a category error, not a rounding difference.

Location source changes the effective geometry

locationSource interacts with the geometry independent of the matching semantic:

GPS-derived: typically 5–20 m accuracy outdoors, degrading indoors and in urban canyons. The geometry is matched close to as-drawn.
IP-derived: resolves to an ISP allocation block, often centroid-biased to a city or zip centroid rather than the device's true location — a device can match a 1 km geofence from tens of kilometers away if the IP registry entry is stale or the ISP routes traffic through a distant node. See ip-derived-location.
Publisher-declared: the location is asserted by the publisher (a weather app's "current city," a news site's regional edition) with no device-level signal at all. Matches at the publisher's declared granularity regardless of the requested geometry's precision.
Cross-device: a household or person graph links a matched device to other devices never directly observed inside the geometry; the executed audience is provably larger than the set of devices that produced a location event.

Lookback window and duplicate eligibility

A device observed inside overlapping geofences during the lookback window is eligible under both. If reporting sums audience per fence rather than taking the union, the same device is counted twice — this is duplicate-observations, and it inflates reach numbers proportional to fence overlap and lookback length. The mitigation is to deduplicate by a stable device key within the reporting window before aggregation, and to report the union's cardinality, not the sum of per-fence counts.

Treatment/control contamination and excluded-area leakage

For measurement, not just delivery, matching semantics create contamination paths that geometry alone does not reveal:

A recent_presence semantic with a long lookback pulls people who moved out of the control area into treatment eligibility retroactively, and vice versa.
An excluded area (a competitor's exclusive zone, a control market) built from physical_presence still leaks devices matched by home_location or interest, because those semantics do not require the device to have been physically inside the excluded polygon at all.
Bidstream truncation: real-time bidstream feeds frequently omit or coarsen the location field below a documented threshold to save payload size or to satisfy consent constraints, so a physical_presence match computed from bidstream is silently biased toward the subset of impressions that still carried usable coordinates.

Consent state (see privacy-and-minimum-aggregation) can force a platform to degrade locationSource precision or drop the location field entirely for a given user, without changing the requested geometry. The safe behavior is to treat a consent-reduced observation as a lower-confidence match — never to up-sample it back to the original geometry's resolution, and never to silently exclude it from reach denominators without disclosure.

Assumptions and limitations

This model assumes the platform discloses matchingSemantic and lookbackWindow per line item; when a platform reports only platform_defined, downstream comparison across platforms is not valid without an independent audit, and any coverage or overlap metric computed from the geometry alone should be labeled as an upper bound on delivered match rate, not the match rate itself.