Should you use subdomains or subdirectories when creating multiple websites under one domain? 
This is a recurring question, so let me treat it here with more attention.

First you have to understand that subdomains are considered by Google as different domains.
e.g.:
http://my1.ideasbeta.com
http://my2.ideasbeta.com
http://my3.ideasbeta.com

are considered as 3 domains
whereas

http://www.ideasbeta.com/my1
http://www.ideasbeta.com/my2
http://www.ideasbeta.com/my3

are obviously considered as 1 domain.

When you do a search on google, it tries to find the correct results into its database for EACH domain.
So let’s say you have 10 subdomains with some similar content, you might appear ten times in Google results (I said similar, non duplicate).
And if you have the same content on one domain with subdirectories, you will be displayed one time.

Do you start to see the advantages of using subdomains?
Be careful though to create several pages on each subdomain. If you just create many subdomains with only a few pages, it can be considered as spam by Google.

Now if you think that subdomains are considered as different domains, another interesting (mis-)use is to have many subdomains, all of them indexed through links on other “trusted” websites.
Then have all the subdomains point to one main domain. Voila, you get a powerful link building technique.

Tags: blackhat, SEO, online marketing, monetization, make money, grayhat

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