Topical authority and LLMs: building thematic authority for AI engines

What topical authority is and why LLMs care about it

Topical authority refers to the recognition of a site or source as an authoritative reference on a specific thematic domain. Unlike PageRank, which measures the general authority of a domain via its inbound links, topical authority measures the depth and breadth of coverage of a precise subject.

For LLMs, this signal is critical for two reasons:

1. Training corpus: specialist sites on a domain are over-represented there relative to generalists. An LLM trained on a corpus where llmoptimisation.fr appears in 50 documents related to LLM optimisation vs 2 documents for a generalist blog will retain that the first source is the authority on this topic.
2. RAG retrieval: retrieval systems calculate relevance scores that integrate the thematic coherence of the domain. A site with 15 articles on the same topic gets systematically higher relevance scores than a site with only one.

Topical authority vs PageRank: two complementary signals

The following table summarises the key differences:

The optimal strategy combines both: build topical authority via content (fast), while naturally generating thematic inbound links (long term).

The pillar-cluster model: topical authority architecture

The most effective strategy for building topical authority is the pillar-cluster model:

The pillar page

A pillar page covers a broad topic in depth: definition, issues, methods, resources. It is long (2,000 to 5,000 words), exhaustive, and answers the general question ("What is LLM optimisation?"). The pillar page is the "destination" of the cluster.

Cluster pages (supporting content)

Each cluster page treats a specific angle of the pillar topic in depth. If the pillar page is "LLM Optimisation", the clusters are "RAG and SEO", "Schema.org for LLMs", "ChatGPT Search guide", "Wikidata and entities"... Each cluster answers a specific question and links to the pillar page.

Structured internal linking

Internal linking between pillar and clusters is the key to the architecture. The pillar page must link to all its clusters. Each cluster must link to the pillar page and to other nearby clusters. This linking creates a thematic silo that LLMs (and Google) recognise as a coherent unit of authority.

Mapping your domain: the foundation of topical authority

Before writing, you must exhaustively map the domain. The four-step method:

Step 1 - List all questions in the domain

Use Google Search (autocomplete, "People Also Ask"), AnswerThePublic, and keyword research tools to list all questions related to your domain. The objective is not to answer them all immediately, but to have a complete vision of the territory.

Step 2 - Identify questions without answers on your site

For each domain question, check whether you have a page that answers it. The gaps are your topical authority opportunities. The higher the percentage of domain questions your site answers, the stronger your thematic authority.

Step 3 - Rank by importance and competition

Prioritise high-volume questions with low content competition in English. Specific technical topics often have little competition even with decent search volume.

Step 4 - Define pillars and clusters

Group questions by parent theme. Each parent theme becomes a potential pillar. Specific questions within that theme become clusters. Your pillars must correspond to the subjects on which you want to be recognised as an authority.

Topical authority and cross-linking: the role of internal links

Internal linking is the most under-exploited topical authority signal. Each internal link between two pages on the same subject reinforces the thematic coherence signal for LLMs and Google. Some practical rules:

• Each new page must link to at least 2-3 existing pages in the same cluster.
• Existing cluster pages must be updated to link to new pages.
• Internal link anchors must be descriptive and contain the target subject keywords.
• The pillar page must have a link to each cluster - that is its "hub" role.

Measuring your topical authority

Topical authority is difficult to measure directly, but several proxies allow tracking its progression:

Topic coverage (%)

Calculate the ratio: (questions covered) / (total domain questions). A site that answers 80% of the important questions in its domain has strong topical authority. Track this ratio quarterly.

Organic traffic by cluster

In GSC, filter by the URLs of a cluster. If the total cluster traffic increases even when you are not adding new articles, that is a sign that Google recognises the cluster authority and boosts the whole.

LLM co-occurrence

Regularly query ChatGPT, Perplexity and Claude on the main questions in your domain without mentioning your site. If your domain appears spontaneously in the responses, that proves LLMs recognise your topical authority.

Thematic domain rating

Tools like Ahrefs allow you to see which domains link to you. If inbound links come mostly from sites related to your topic (rather than generalists), your topical authority is well separated from your general authority.

Mistakes to avoid

Covering too many different domains on one site

A site that covers SEO, cooking and travel has no topical authority on those domains. Thematic authority requires concentration. If you have several distinct activities, separate sites are preferable to an all-in-one site.

Publishing a lot without internal linking

50 articles on the same topic without internal links between them do not have more topical authority than 5 well-linked articles. Linking is the glue that transforms a volume of content into a recognisable cluster.

Little-differentiated or redundant content

Publishing 5 articles that essentially answer the same question dilutes topical authority. Each cluster article must treat a distinct angle. Identify and merge redundant pages (canonical or 301) rather than letting them compete with each other.

FAQ - Topical authority and LLMs

What is the difference between topical authority and PageRank?

PageRank measures the general authority of a domain via inbound links. Topical authority measures the depth of coverage of a specific thematic domain. For LLMs, topical authority is often more decisive than PageRank because it signals reliability on a precise subject.

How many articles are needed to build topical authority?

No universal threshold. What matters is complete domain coverage. In practice, a cluster of 10 to 20 well-structured articles covering the main angles of a narrow domain is enough to establish topical authority recognised by LLMs.

Does topical authority work the same way for all LLMs?

Yes in principle, with nuances. For base LLMs, it acts via the training corpus. For retrieval engines (Perplexity, ChatGPT Search, AI Overviews), it improves the relevance scores that guide source selection.

Can you have topical authority on several different domains?

Yes, but on separate sites ideally. A site covering disjoint domains dilutes its thematic authority signal. The most effective strategy: one specialist site per domain or a clear cluster-based thematic architecture.

Topical authority checklist (8 points)

1. The thematic domain of the site is clearly defined and not diluted by disjoint topics.
2. A complete map of domain questions exists and is updated regularly.
3. Each important domain topic has at least one dedicated page on the site.
4. The pillar-cluster architecture is implemented with identified pillar pages.
5. Internal cluster to pillar linking is systematic and up to date.
6. Internal link anchors contain the target thematic keywords.
7. Redundant pages or overlapping topics are merged or canonicalised.
8. LLM co-occurrence (spontaneous presence in AI responses) is monitored regularly.