Topical Authority: myth or reality?
Be careful with the concept of Topical Authority when arguing for SEO recommendations. The concept doesn’t stand on a robust logic.
Topical Authority is one of many SEO ghost concepts that are often used to justify recommendations. Some even call it the future of SEO. Funny enough, most articles about Topical Authority recommend doing other SEO things like building relevant links, optimizing on-page factors, or targeting user intent when it comes to optimizing for Topical Authority.
The idea makes sense logically but is there really a difference between SEO best practices and optimizing for Topical Authority?
What’s the idea behind topical authority?
The idea behind Topical Authority is by covering all aspects of a topic, sites get a ranking boost because Google sees them as an authority in the space. On the other end of the spectrum would be sites that only touch the surface of a topic. But that’s where things get fuzzy.
What if you cover all facets of a topic in one big article vs. 100 shorter articles? What’s the difference between Topical Authority and relevance? Does Google really see your site as “authority” or “expert” for a topic when you write a lot of content about it?
How Google could understand topical authority
Let me summarize and comment on the three most common arguments for how Google could measure Topical Authority.
Option 1: Entities
Google has built an entity graph and topic layer that allows it to map and understand the relationship between concepts. We know that this is true. Google recently published an article in which Pandu Nayak explained that Google uses machine learning (Rankbrain) to understand “how words relate to concepts.” 
Advocates of Topical Authority imply that Google uses the entity graph to assess how well a piece of content covers a topic. However, Rankbrain is used to understand how relevant a keyword is for a certain topic/result, not the other way around. It’s a Natural Language Understanding (NLU) algorithm that helps Google serve better results, but it doesn’t evaluate content by how well it covers important entities (at least as far as we know).
Option 2: Neural Matching and Neural Embeddings
Next in line is Neural Matching, a machine learning technology that allows Google to understand “how queries relate to pages”.
“Neural matching helps us understand fuzzier representations of concepts in queries and pages, and match them to one another. It looks at an entire query or page rather than just keywords, developing a better understanding of the underlying concepts represented in them.” 
Aha! Isn’t that what we’re looking for here? Not exactly. Neural Matching helps Google to understand whether a piece of content is relevant for a query and how much. However, it doesn’t say anything about measuring “authority” or “expertise” on the domain level by how much of a topic that domain covers.
Option 3: Backlinks and Internal links
One valid question to raise is whether Topical Authority is driven by content or by links. We invented concepts like Domain Authority (not a metric Google actually uses) that sound fairly similar to Topical Authority. So, could Topical Authority be the result of backlinks?
Backlinks certainly demonstrate “authority”, especially from relevant and trustworthy sources. I don’t see covering all aspects of a topic as the driver of links. I’ve seen many links go to outstanding and interesting content. I’ve never seen someone link to another site because “it covers a topic holistically.”
Internal links are also powerful relevance signals to search engines. The way I can see Topical Authority working out is that by covering all aspects and subtopics of a topic, you simply create more content around the same topic. As you link more between these articles, you simply send more signals to search engines from and to relevant pages. This is the only recommendation of “building more Topical Authority” that makes sense to me.
How to approach Topical Authority as an SEO
The point about this article is that we shouldn’t look for “magical concepts” in SEO and instead go back to first principles. But another point I want to make is that covering all aspects of a topic is still a good idea and matters more than whether Topical Authority really exists and how Google measures it.
It’s beneficial for users and businesses because when you cover all aspects of a topic and do it well, there are fewer (maybe no) reasons for users to leave your site and that is big.