Recently, Google has announced a change in its treatment of subdomains and how they are represented in their search result pages.

In the past, subdomains such as:


example.com
phones.example.com
furniture.example.com
yoyos.example.com


have all been treated as separate hostnames. To explain why this might be an advantage to you the website owner, you need to know how Google have treated these separate hostnames in the past.

Subdomains vs. Subdirectories

When Google displays the results of a search query, it will only return a maximum of two relevant searches results per hostname. This behaviour is called ‘host crowding’ and it means the user will have exposure to more than a single website for a search term.

A subdirectory, or a folder, will be considered part of the top level domain so this additional content or categories will still only show two results per search term on the result page.

Subdomains however, get around this limitation because they are being treated as a unique hostname. This means one top level domain can potentially dominate search engine result pages with all of their own content, depending on how many subdomains they might have that are relevant to the search term.

What does this actually mean?

This is another great move by Google to enhance the usability of the search engine user by trying to eliminate people from gaming the system.

In many instances, websites with multiple subdomains are not actually causing a problem and apparently won’t be filtered by this new algorithm change. (these have been classed as ‘exceptions’ by Google).

Websites such as Ebay or About.com that are extremely large and categorise their content with the logical architecture of subdomains. These categories will not always compete for every search query, so they can potentially return relevant results for the user.

Who this will target is the SEOs and websites owners who have been on to this ‘white hat’ technique for years. Websites with URLs such as:


example.com
brand1.example.com
brand2.example.com
brand3.example.com


that produce duplicate or syndicated content across several subdomains will start to feel the filtering affects of this algorithm.

Using subdomains to distribute content that is not different or categorised in a logical manner will now cause you to have less control in the way that Google will display the results of your website to potential users.

Who benefits from this?

I think a few people will benefit from this and it’s a good move if implemented correctly and does not filter out relevant websites that use subdomains correctly.

Smaller websites have often been disadvantaged by the treatment of subdomains by Google. I have worked with many websites that didn’t have enough content to be splitting it up with subdomains, but were often bound by third party contracts or server configurations.

This change will mean that those websites that have been diluting their Page Rank for so long will have a bit more clout with the search engines as a single hostname for all of their content. These small websites might be able to think about using subdomains to retain simplicity and enhance branding without worrying about this Page Rank issue anymore.

The user also benefits from a more concise, accurate search result provided by Google who continues to impress me with concern for the individual search engine user. It’s a real pain for some SEOs and website owners whenever Google changes it’s algorithms like this, but I am still convinced it’s for a good reason.

As with anything SEO related, if you use subdomains strictly to create more visibility in the search engines for your website, then you are probably using them for the wrong reason.