A radius target is a circle. One coordinate pair fixes the centre, one distance sets the edge, and advertisements serve to devices judged to sit inside the resulting area. Platforms also call it proximity targeting. It exists because commercial catchments rarely match administrative boundaries: a bakery draws from a few streets in every direction, a car dealership from half a county, and neither shape appears on a map of cities, postcodes or television markets.

The circle is the crudest available model of a catchment, which is part of why it survived. Two numbers define it, any point on the planet can anchor it, and no vendor has to maintain a boundary file to support it.

How the circle is defined

In Google Ads the object is called ProximityInfo. Four fields carry it: geo_point, holding latitude and longitude expressed in micro degrees; radius, a decimal number; radius_units, which defaults to kilometres; and address, described in the API reference as a label that does not affect ad serving. Either input works. Supplying an address computes the coordinates; supplying coordinates leaves the address as an unvalidated note.

Floors come from privacy policy rather than geometry. Google's help documentation states that radius targeting under 1 km around any given location is not permitted, because location targets must clear minimum area and minimum user count thresholds. Hotel Ads campaigns cannot be targeted by radius at all. One asymmetry shapes account structure: the Google Ads API allows a location to be excluded by setting a negative flag on a LocationInfo object, but that flag is not available for proximity criteria. A circle can be bought. It cannot be cut out.

Demand-side platforms handle the same shape at higher volume. Display and Video 360 splits geography targeting into regional lists and proximity lists, and a proximity list accepts up to 10,000 street addresses or latitude and longitude pairs pasted line by line. The default target radius is 20 miles. The documented minimum is 1 kilometre, and the area must contain a population of at least 1,000, with a larger radius substituted where that threshold is not met. Google's Studio product applies a different range for creative selection, allowing a custom radius from 1 km to 2,000 km and ordering matched feed rows from nearest to furthest.

Historic minimums ran far tighter outside the large platforms. PPC Land's location marketing guide recorded that demand-side platforms and location vendors typically supported a minimum radius of around 50 metres, available only in in-app environments where coordinates were present in the bid request.

What actually places the device

The circle is exact. The position tested against it is not.

In OpenRTB, location travels in the Geo object. Latitude and longitude sit alongside type, recording the source of the reading, and accuracy, an integer in metres recommended when coordinates come from a device's location services. Two further fields describe provenance: lastfix, the number of seconds since the fix was taken, and ipservice, naming the vendor behind an IP lookup. Documentation for Google's Authorized Buyers integration states that Google sources device locations only from IP geolocation, never from satellite positioning, and never populates type, accuracy, lastfix or ipservice in either protocol. A buyer reading Google supply therefore receives a coordinate with no stated provenance and no stated error.

Browser-side, the unit of accuracy is itself a radius. The W3C Geolocation API exposes an accuracy value defined as the 95% confidence radius in metres around the reported point. Android's platform location API defines its own accuracy figure as a 68% confidence radius, so identical numbers from the two sources describe different probabilities. Chrome on Android added an approximate location permission in May 2026, capping precision before coordinates reach a site; the underlying coarse permission resolves to roughly 1.5 kilometres, around three city blocks.

Where coordinates are absent, IP inference fills the gap, and it performs badly. Research commissioned by the Coalition for Innovative Media Measurement and Go Addressable, published on 5 November 2025, put IP-to-postal accuracy at 13% across nearly a billion records. FreeWheel, drawing on the same data in February 2026, argued that IP-based targeting can miss 87% of households, with state-level accuracy ranging from 5% to 17% and border regions performing worst. Adstra and InterMedia Advertising reported in July 2026 that 23% of residential IP addresses reached the intended geographic target. Each of those figures comes from an organisation selling a remedy.

Origin and evolution

Google began testing regional AdWords targeting in October 2003, initially against Nielsen's designated market areas in the United States. Worldwide radius buying followed in 2004, when Google added what it then called customised targeting: an advertiser entered an address or a latitude and longitude pair and set a distance. As ClickZ reported at the time, the minimum was 20 miles, or 35 kilometres, a floor wider than many cities. The 1 km minimum in force today is a twentieth of that distance.

Bid control arrived with enhanced campaigns, announced on 6 February 2013, which allowed location bid adjustments inside a single campaign rather than requiring one campaign per area. Google Ads scripts still expose a bidModifier argument alongside latitude, longitude, radius and units.

Measurement standardised the vocabulary next. The Media Rating Council, with the IAB and the Mobile Marketing Association, issued Location-Based Advertising Measurement Guidelines on 29 March 2017 defining two fence types: point-radius, a circle around coordinates, and boundary measurement, a polygon traced around the premises. The same document placed satellite accuracy at 10 to 100 metres and Wi-Fi at 30 to 100 metres, and noted that fences generally cannot represent multi-storey structures.

Display and Video 360 added proximity targeting to location lists in an April 2023 release. Automation moved in the opposite direction. Performance Max campaigns with store goals apply a dynamic radius automatically, and Google has discouraged layering conventional geographic targets on top. Waze advertising, extended to 41 countries including all 27 European Union member states in September 2026, either takes a radius set in the campaign or computes one from vertical, population density, competitors and a driver's travel preferences.

Why the shape matters commercially

Area grows with the square of the distance. A 10-mile radius covers four times the ground of a 5-mile radius, not twice, so doubling a setting quadruples the population in scope and the budget needed to reach it at comparable frequency. That arithmetic is invisible in an interface that asks for a single number.

Claims made about the circle now carry legal weight. Final orders issued by the Federal Trade Commission on 26 August 2026 placed three vendors under 20 years of substantiation duties over geographic targeting representations, after a product sold as detecting purchase intent from nearby conversations turned out to deliver brokered email lists with coverage unrelated to the territories bought.

Limitations and disputes

A circle models a catchment badly wherever geography is not uniform. Rivers, motorways, borders and one-way systems cut drive times that the shape ignores. Location vendors have long offered polygons as the alternative, and the trade-off is concrete: a generous radius around a mall entrance captures passers-by, while a tight polygon around a single storefront misses people arriving from another side.

Regulation has now adopted the radius as its own unit of harm. The stipulated order closing the Commission's Kochava case, signed on 4 May 2026, defines precise location data down to a 1,850 foot radius. Vermont's Act 138, signed on 16 June 2026, uses the same 1,850 foot figure in its data broker rules. The draft SECURE Data Act, introduced on 21 April 2026, treats geolocation inside 1,750 feet as sensitive data, the same threshold Virginia used when banning sales of precise geolocation from 1 July 2026. Washington's My Health My Data Act, effective 31 March 2024, bans geofencing within 2,000 feet of an in-person care facility outright. Tight circles are where targeting and regulated surveillance converge, a proximity underlined by federal interest in advertising geofencing tools for investigative work.

The measurable objection is simpler. A radius set at 1 kilometre implies confidence in a position whose stated error, where any is stated, is frequently larger than the target itself.

Not the same as

A geofence is the general boundary concept and covers any shape. A radius is the circular case of it, which is why measurement guidance separates point-radius from boundary fences.

A polygon traces an actual footprint. It costs more to produce and maintain, and it is what aggregated geographic products increasingly ship: microm data reaching Azerion's platform arrives as map polygons averaging about 500 households.

Designated market area targeting buys Nielsen's 210 county groupings, fixed boundaries built for broadcast signal reach rather than driving distance.

Location of interest targeting is not geographic presence at all. Google infers it from query terms, past searches, Maps activity and page context, and it is not restricted to the searcher's country.

Recent developments

Google has been removing the circle from its local products while keeping it in paid media. Business Profile service areas are now entered as named places rather than shapes, with radius areas retired and legacy entries locked from editing. Radius targeting survived the removal of language targeting from search campaigns, remaining available alongside countries, regions and cities.

Signal supply, meanwhile, is being contested from both ends. Browsers are capping precision, statutes are defining it in feet, and device makers are being caught supplying it without a satellite receiver: packet captures published in September 2026 showed an LG television reporting street-level position to its advertising subsidiary roughly 20 times a minute.

Timeline

  • October 24, 2003: Google begins beta testing regional AdWords targeting in the United States
  • 2004: AdWords adds customised targeting worldwide, with a minimum radius of 20 miles or 35 kilometres
  • February 6, 2013: Enhanced campaigns introduce location bid adjustments within a single campaign
  • March 29, 2017: The MRC, IAB and MMA publish Location-Based Advertising Measurement Guidelines defining point-radius and boundary fences
  • March 31, 2024: Washington's My Health My Data Act bans geofencing within 2,000 feet of an in-person care facility
  • April 2023: Display and Video 360 adds proximity targeting to location lists
  • November 5, 2025: CIMM and Go Addressable publish IP linkage accuracy research
  • April 13, 2026: Virginia signs SB 338, banning sales of precise geolocation inside 1,750 feet from July 1
  • April 21, 2026: The SECURE Data Act is introduced, defining precise geolocation at a 1,750 foot radius
  • May 4, 2026: The FTC's Kochava order defines precise location data down to an 1,850 foot radius
  • May 2026: Chrome on Android adds an approximate location permission for websites
  • June 16, 2026: Vermont's Act 138 sets an 1,850 foot radius in its data broker rules
  • July 15, 2026: Adstra and InterMedia report 23% geographic accuracy for residential IP addresses
  • August 26, 2026: The FTC issues final orders imposing 20 years of substantiation duties on geographic targeting claims
  • September 2026: Waze advertising expands to 41 countries with automatic radius calculation

Summary

Who. Advertisers and agencies set radius targets; Google Ads, Display and Video 360, Meta and mapping platforms implement them; location vendors supply the coordinates and the fences; regulators now define the distances that count as precise.

What. A radius is a circular targeting area defined by a centre point, a distance and a unit, expressed in Google Ads as a ProximityInfo criterion and in Display and Video 360 as a proximity location list.

When. Regional targeting entered beta in October 2003, distance-based buying arrived in 2004 with a 20 mile minimum, measurement definitions followed in 2017, and statutory definitions measured in feet arrived between 2024 and 2026.

Where. In campaign settings on search, display, video, audio and mapping inventory, in the Geo object of an OpenRTB bid request, and in the permission layer of browsers and mobile operating systems.

Why. Catchments do not follow administrative boundaries, and the circle is the cheapest shape that approximates one. Its weakness is that precision in the setting implies precision in the signal, and the signals placing devices inside the circle are measured in confidence radii that are often wider than the target.