SiteFocus, siteRadius and topical authority in SEO

Topical authority is not a “content attribute”.
It is a property of an entire document system, evaluated relationally — both internally and against queries, and even against the user behaviors that follow those queries.

The Google documentation leak (Warehouse API) does not “confirm” topical authority as a single ranking signal. It reveals something more important: how topical concentration and document-level deviation from a topical core are measured algorithmically.

Two metrics illustrate this mechanism particularly well:

• SiteFocusScore
• SiteRadius

These are not SEO metrics “to be optimized”.
They are components of a system used to evaluate source coherence and specialization.

TL;DR

• Topical authority is not a content attribute but a property of an entire document system.
• Google measures topical coherence using semantic embeddings, not keywords.
• SiteFocusScore reflects how tightly a site converges around a single semantic domain.
• SiteRadius reflects how much individual documents drift away from that domain.
• These metrics are not optimization targets; they are internal evaluation mechanisms.
• Topical authority emerges when:
  • topical coverage is coherent and entity-centered,
  • content satisfies real user intent,
  • user behavior validates usefulness over time.
• User signals validate quality after semantic pre-filtering, not before.
• Mass-producing thematically aligned but useless content increases SiteRadius and fails long-term.
• Topical authority behaves more like a threshold than a linear scale.
• Architecture, pruning, updates, and intent alignment matter as much as content itself

SiteFocusScore and SiteRadius – what they actually measure

SiteFocusScore – topical concentration of a content system

SiteFocusScore describes how strongly a site’s content converges around a single semantic domain.

This is not about:

• keyword frequency (keyword stuffing),
• manually assigned categories,
• thematic declarations on an “About” page.

It is about vector-level semantic convergence between documents within a domain.

The higher the coherence:

• conceptual,
• entity-based,
• intent-based,

the higher the SiteFocusScore.

This is a domain-level metric, not a page-level one.

SiteRadius – deviation of individual documents

SiteRadius works in the opposite direction.

It measures:

• how far a given page semantically “drifts” from the site’s topical core,
• whether a document reinforces or dilutes the main theme.

A high SiteRadius indicates content that is:

• incidental,
• opportunistic,
• created “because there was a keyword”.

The content does not have to be low quality.
It is enough that it does not fit the overall topical vector of the site.

How Google calculates this – embeddings instead of words

The question “how does the algorithm know something is close to or far from a topic?” is incorrectly framed.

Google does not compare topics descriptively.
It compares vector representations of meaning.

The documentation explicitly references:

• pageEmbeddings – a semantic vector representing a document,
• siteEmbeddings – an aggregated semantic vector representing the entire site.

The relationship between them is calculated mathematically (e.g. cosine distance).

This means one thing:

• topical authority is not an algorithmic opinion,
• it is the result of calculations in semantic space.

Why Google measures topical concentration

Not to “penalize multi-topic blogs”.

The purpose is to answer fundamental system-level questions:

• Does this entity (author, brand, editorial team) actually specialize in a given domain?
• Which documents belong to that specialization, and which are peripheral?
• Can the site be treated as a stable knowledge source, or merely a collection of incidental content?

These signals are used:

• in ranking,
• in indexing,
• in retrieval systems (especially LLMs and AI Overviews),
• in quality evaluation layers.

Topical authority is an emergent effect of a coherent content system, not a separate metric to be “boosted”.

Topical authority and user behavior

Google has repeatedly acknowledged (including in DOJ testimony) that:

• quality predictions are uncertain,
• user behavior is used for validation.

Source: https://hexdocs.pm/google_api_content_warehouse/api-reference.html

But this happens at a second stage.

First, a candidate set must be constructed:

• documents,
• sources,
• entities.

This cannot be done using keyword matching alone.

That is why:

• SiteFocusScore,
• SiteRadius,
• entity coherence,

are required as a pre-filtering mechanism.

Important context: topical authority ≠ topical similarity alone

Topical authority is often also understood as comprehensive coverage of a domain in the practical context of a specific intent and the entity that satisfies it (brand as a “source context”), additionally validated by users through behaviors indicating satisfactory Google sessions.

This is how it is framed in Koray Tugberk Gubur’s methodology:

topical authority = topical coverage × user signals

This is a crucial addition, because many publishers mass-produce content that is thematically aligned but completely useless.

Such sites often experience short-term growth, only to lose visibility during the next core update.

That is why brand content — even when supported by AI — must be:

• brand-specific,
• genuinely useful,
• designed to lead users to meaningful next steps.

Why “covering the topic” works — but not the way the industry thinks

This is not about:

• the number of articles,
• encyclopedic completeness.

It is about whether:

• the topical core is clearly defined,
• all documents reinforce the same semantic vector,
• secondary topics are contextually embedded rather than autonomous.

Example:

If you sell chandeliers:

• you write about chandelier types,
• installation,
• selection criteria,
• comparisons.

You do not publish general interior design advice as a separate topic.
You may reference it only in relation to chandeliers.

This is the difference between:

• expanding a topical map,
• and increasing SiteRadius.

EffortScore, ChardScores, and the problem of “easy” content

The leak also references effort and usefulness signals, including:

• EffortScore – the effort invested in content creation (how much it differs from a wall of generic AI-generated text based on training data),
• ChardScores – freshness plus user engagement.

This highlights a hard limitation:

topical authority cannot be built with low cognitive cost.

Content that is:

• generic,
• easy to generate with LLMs,
• lacking information gain,

may perform temporarily, but it:

• does not stabilize SiteFocusScore,
• does not hold up long-term,
• fails during quality updates.

That is why:

• content pruning,
• updates (especially for content targeting high-QDF queries),
• real usefulness,

are required to maintain topical authority — not just to build it.

Topical authority – scale or threshold?

In practice, this is not a linear scale.

It behaves more like a decision threshold:

• either the site is treated as a topical source,
• or it is not.

Within that boundary, competition happens on:

• quality,
• coherence,
• depth of intent understanding.

It is not enough to “write about everything in a topic”.
What matters is precise anchoring in a single primary entity.

It is very likely that:

• the homepage,
• information architecture,
• brand context,

play a dominant role here.

Content architecture as a decision system

Topical hubs, silos, and clusters are not “SEO structures”.

They are:

• mechanisms for limiting SiteRadius,
• mechanisms for reinforcing SiteFocusScore,
• mechanisms for guiding users through logical decision paths.

Internal linking is not for crawlers.
It exists to maintain cognitive coherence:

• for users,
• for retrieval systems,
• for LLMs that consume content fragmentarily.

CTAs, content sequencing, and inter-document dependencies are all part of the same system.

Why weaker domains sometimes outperform “stronger” ones

If you see a site that:

• has a smaller backlink profile,
• lacks an obvious “brand” in tools like Ahrefs,
• yet dominates a niche,

it is often because it has:

• a higher SiteFocusScore,
• a lower SiteRadius,
• better intent alignment.

Links still matter.
But contextual relevance — including link context — can offset quantitative disadvantages.

Operational conclusions (no checklists)

• Think of topical authority as a system property, not a content feature.
• Narrow your topic instead of expanding it.
• Treat information architecture as a semantic control mechanism.
• Remove or consolidate content that increases SiteRadius.
• Update and deepen content that reinforces the topical core.
• Do not attempt to “scale” topical authority through automation.

SEO, AI Overviews, and LLM retrieval operate on the same underlying logic.
If the content system is cognitively coherent, it will perform across all layers of organic discovery.

Topical authority is not a myth.
It is a byproduct of a well-designed knowledge system.

Short Q&A on SiteFocus, SiteRadius and topical authority

Is topical authority a ranking factor?
No, it is an unofficial system-level effect / status that influences ranking, indexing, and retrieval decisions indirectly.

Can topical authority be optimized directly?
No, it emerges from semantic coherence, not from explicit optimization.

What does SiteFocusScore measure?
It measures how strongly a site’s documents converge around a single semantic space (unique centroid).

What does SiteRadius measure?
It measures how far individual documents deviate semantically from the site’s topical core.

Are these metrics page-level signals?
No, they operate primarily at the domain or system level.

Does keyword overlap build topical authority?
No, topical authority is based on embeddings and meaning, not keyword repetition.

Do user signals create topical authority?
No, they validate or invalidate it after semantic pre-filtering.

Can AI-generated content build topical authority?
Only if it adds brand-specific information gain and fits a coherent content system.

Is topical authority about content volume?
No, adding volume without coherence usually increases SiteRadius.

Why do low-link sites sometimes win?
Because strong semantic focus and intent alignment can offset weaker link profiles.

Is topical authority linear or binary?
In practice, it behaves more like a threshold than a smooth scale.

What increases SiteRadius the most?
Publishing opportunistic content that is topically adjacent but contextually autonomous.

Is architecture part of topical authority?
Yes, information architecture controls semantic flow and limits topical drift.

Can topical authority decay over time?
Yes, through outdated content, semantic noise, and unvalidated user satisfaction.

What is the biggest misconception about topical authority?
That it is something you can “optimize” rather than design for structurally.