How can I link subdomains to my main domain to get the SEO benefit? I've seen examples using all sorts of clever redirects and PHP where you get the subdomain's content on the main site...but what I want is for the subdomain to be linked with the main domain; I don't mind it sitting by itself, but I'd just like to get the SEO benefit of it. I'm aware that Google see subdomains as separate domains but can change / help them to be seen more as one site?
My personal preference on subdomains vs. subdirectories is that I usually prefer the convenience of subdirectories for most of my content. A subdomain can be useful to separate out content that is completely different. Google uses subdomains for distinct products such news.google.com or maps.google.com, for example. If you’re a newer webmaster or SEO, I’d recommend using subdirectories until you start to feel pretty confident with the architecture of your site. At that point, you’ll be better equipped to make the right decision for your own site.
Subdomains SOMETIMES inherit and pass link/trust/quality/ranking metrics between one another
Subfolders ALWAYS inherit and pass link/trust/quality/ranking metrics across the same subdomain
Google will automatically treat the subdomain as part of the main domain if it thinks they are part of the same site and run by the same person or company. Here are some signals that you can use to make it easy for Google to see that they are part of the same site and run by the same person:
- Interlink the main site and the subdomain. Separate sites don't typically interlink.
- Use the same copyright statement on both.
- Register both in Google Webmaster Tools. This shows that the same author has access to both.
- Get HTTPS certificates for each of them (or use the same wild card certificate)