How Does Google Handle Subdomains?

Google treats subdomains the same as subdirectories.

A subdomain is a method of addressing part of a website so that it appears to be a different website. The subdomain has the same domain name as the main site, but it has a prefix. This enables website administrators to cut out complicated addresses, particularly those that involve a series of directories and subdirectories. But what effect does “appearing” to be a different site have on the way Google allocates the count of visitors to that site?

Main Site

Google treats the standard “www” as a subdomain. The main domain of your site will always be accessed as “domain.com” and Google treats this as a separate address to “www.domain.com,” even though traditionally the two are regarded as the same. It is important to merge these two sites by creating a 301 redirect from one to the other. This way visitors will always be taken to common content. Google declares that these two addresses may have different content.

Subsites

A subdomain replaces the “www” part of a domain name with a different code or keyword. This can help to better organize access to subdirectories of a site. For example, www.domain.com/content/sections/news involves a lot of typing and can be cut to a shorter version by creating a subdomain of news.domain.com.

Set Up

Although there is a complicated method for manually writing subdomain information in a configuration file, most websites are administered though cPanel and this has an easy to use interface for defining subdomains. The subdomain maps to a directory in the website structure. The administrator creates the subdomain -- in this example, news.domain.com -- by entering it in the subdomain setup screen. The news directory path -- in this example, www.domain.com/content/sections/news -- is entered as the home directory of the subdomain.

Google and Subdomains

Since December 2007, Google has treated subdomains the same as subdirectories. Before that date, a site could get several entries in the search results relevant to its topic by creating subdomains. Google treated subdomains as separate sites. Google limits a site's appearance to just two entries per result, so websites could flood a results page with many entries by creating subdomains and circumventing the two entries rule. The 2007 rule change removed that advantage from subdomains. Since then, there has been no difference, in terms of Google results, between subdomains and subfolders.

Consolidation

Google evolved its handling of many pages belonging to the same site in search results. The company came to the strategy, in 2011, of allowing many entries from the same site in a search result. Google now presents all pages on a site that are relevant to the search query, but groups them together as one main entry for the home page of the site with two columns of pages beneath. Google places a limit of 12 indented entries per site. Each entry gets a very brief description. The 2007 decision of treating subdomains as part of the same domain still holds under this new system.

References

• Search Engine Land; Sub Domains to Be Treated as Folders by Google; Barry Schwartz; December 2007
• Matt Cutts: Subdomains and Subdirectories; December 2007
• Search Engine Land; New: Google Classifies Subdomains as Internal Links Within Webmaster Tools; Barry Schwartz; September 2011
• Search Engine Land; Official: Google Sitelinks Expands to 12 Pack; Barry Schwartz; August 2011