In a recent Webmaster Help video, Google’s Matt Cutts reported that adjustments to Google’s search algorithms have removed many of the advantages given to sites organizing content using subdomains rather than a subdirectory.
A subdomain appears as such: “http://www.blog.brafton.com”.
A subdirectory looks like this: “http://www.brafton.com/blog”.
According to Cutts, subdomains may have traditionally held special SEO appeal, because brands using multiple subdomains could see more results on given SERPs. However, this is no longer the case.
“The historical context is that we used to crowd by what we called ‘host,’ which is essentially a subdomain, and we would only allow two results on each host,” Cutts said. “In that situation, it might make sense to have more subdomains because you can get two results from one host name and two results from another subdomain.”
Cutts said webmasters frequently abused this feature by creating a number of subdomains for the same types of content aimed solely at generating more links to their sites (and dominating SERPs). Adjusting algorithms to treat subdomains and subdirectories prevented webmasters from abusing the practice. As such, Cutts advises webmasters and marketers concerned with URL structure for both SEO and optimum user experience to structure links in whichever format is most convenient for them.
Last year, Brafton highlighted Google’s adjustment to subdomains, which essentially reclassified them as internal links. As such, Cutts’ statement that Google is treating subdomains and subdirectories similarly for the sake of SERP diversity should encourage marketers to choose the format and site structure easiest for them. An in-depth SEOmoz post offers some other insights on the benefits of organizing website content into subdirectories versus subdomains.