When To Use Subdomains and Folders on Websites

Vanessa - Generally use subfolders to organize your content, as it’s much easier and is treated in a very similar fashion by Google as subdomains. Try to create a flat subfolder structure and don’t create a complicated hierarchy that goes down too many levels.

Use subdomains when you have very disparate content that you feel searchers would feel relevant. For instance, videos are very different from articles, so it may make sense to separate those into subdomains. If you have a travel site, it may make sense to use subdomains to categorize cities. Someone searching for a particular resort may want to see the various locations that reort is located in.

In particular, look at the use of folders vs. subdomains from a business perspective. What makes the most sense for your users? If you have completely different business units, they may appear more credible as individual subdomains. But for related content, a folder structure often makes the most sense. Link.