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Subdomain and subdirectory: what is the best choice for SEO

Subdomain and subdirectory: what is the best choice for SEO?

Within the framework of the development of a group of websites belonging to the same company, which has several "areas" of activities, we were faced with a problem when choosing domain names.

Should we opt for a subdomain or a subdirectory for the sub-sites?

What is the best option for ensuring good SEO? What are Google's answers to this question?

To answer these questions, we had to explore the technical considerations of SEO we had to take into account and decide when it would make the most sense to use them.

Below is our recommendation delivered to the customer.

Understanding subdomains and subdirectories

Before deciding which format to consider, let us first recall the technical difference between subdomains and subdirectories.

A subdomain is a child element of the parent domain. In our case, it is sometimes used to host the sites dedicated to each of the sub-activities of the organization.

Subdomain :
Subdirectory : https://www.notredomaine/activite1

Note that in the example of the subdirectory (also called a subfolder), the /activity1/ element is in the main domain. It is part of the main site, like all the other pages of the same site. 

The subdomain is located outside the main domain.

The site structure has an impact on organic search performance 

In fact, opting for a subdomain rather than a subdirectory for a section of your business may slow your growth. However, in some cases, it makes sense to host your site in a subdomain.

So, it really depends on your strategic choices. For this purpose, let us break down the different usage scenarios and how they can impact your website's organic performance:

Google treats subdomains as separate entities from your main domain since subdomains usually have different content that cannot really be associated with the main site. In some specific cases, subdomains of the main domain are controlled by different teams or individuals.

Thus, is not considered to be part of, but is considered to be a separate entity.

As a result, the content with its valuable advantages, (such as backlinks hosted on a subdomain) is not taken into account by Google's bots when ranking your main domain. 

However, while this may not seem like a good thing, sometimes it makes perfect sense for a subdomain to be considered to be a separate entity from the main domain, particularly when they represent separate companies or divisions.

Google crawls both subdomains and subdirectories 

Google's John Mueller states that: "Searching the web via Google works well, whether you use subdomains or subdirectories." 

So, whether you choose a subdomain or a subdirectory, there will be no concern about Google taking your pages into account.

So, what still needs checking?

To answer this question, we must remember that content and links are among the main factors of Google's ranking.

Hosting airport sites on a subdomain will mean that their content and the links that point to them will not help your main domain to rank higher and get more traffic.

If content and links are split between a subdomain and the main domain, the overall "authority" of these two entities will be lower than if everything belonged to the main domain.

For this reason, it is common to see an increase in visibility and overall organic traffic when migrating relevant subdomains to subfolders of the main domain.

And the practical cases that demonstrate the gain in "authority" of sites that have chosen to change their subdomains into subdirectories are numerous.

The only reasons why you would not choose this option are the following:

  • The sub-sites would be developed using a different language from that of your main site
  • You want to use a dedicated platform rather than integrated sites 
  • A quote form or other feature that cannot be located on the same server as the main site because it is written in different coding languages

Clearly, there is still a lot of confusion about whether subdomains are beneficial to your SEO efforts. A large part of the SEO community agrees that when not facing technical or legal/administrative restrictions, it is better to host your content in a subdirectory rather than in a subdomain.


Ahlem Jaafri

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