Sites You Control
When you own websites, you have a lot of websites you control, this is traditionally known as an administrative relationship, meaning that you are an administrator. You can control the links on the site. You control the content of the site. Maybe these are sub-domains that you own. Maybe these are multiple properties within your business.
The reason that this is so important to Google is because, if you think about the link graph and relationships between sites, links between sites that are controlled by the same person probably shouldn't count as much as links that are editorial and controlled by other people, because when you get links, you want them to be natural and not something that you control.
1. Structure of Related Websites
One example is to distribute the authority between those sites. This also works on a much smaller scale too sometimes, often on sub-domains. You see a lot of blogs being started on subdomains' websites because it's easier from a development point of view or for whatever the reason. You want that sub-domain, that blog to have the same authority as your main site. Now it's oftentimes up to Google whether or not they give that authority to your blog or your sub-domain. But if you can give them signals to tell them, "Yes, this is associated with my main domain," that often goes a long way in helping that sub-domain to rank.
Same with alternate languages. You have French content. You have Spanish content. You have English content. They're all on your site. Maybe they're on a different sub-domain or a different top level domain, but you want Google to know that they have the same authority as your main site that you worked so long to build up.
2. Impact of Related Websites
There's the idea of link schemes in bad neighborhoods. If there are 12 sites, and they're all interlinking to each other, that might be a pretty good signal to Google that it's sort of a link scheme and those links shouldn't count, or they could be penalized.
they find the penalty transferring to that new domain, even though they've cut all the backlinks. They've changed the URL, everything. How does Google know that that's the same site? So these are important questions to ask yourself and help determine: Can you be helped by establishing these relationships between sites, or can you be hurt? If you understand some of the signals Google is using, you can take advantage of this.
3. Signals of Related Sites
Link patterns, when you have, again, a lot of sites linking to each other, and Google has a complete catalog of links or the most complete catalog of links on the web, when you take all this together, using various statistical analysis methods, you can determine pretty closely who's associated with what, who has control over what. These are all things that people are looking at, all that publicly identifiable information.
If you're simply moving your site from one site to another to escape a penalty, that may be not enough if you're using the exact same content and some of those other things, such as similar images. Two images hosted on different sites with the same content could be an indication that the sites are owned by the same entity.
Formatting, CSS, you'll often see sites that are owned by the same individual use a lot of the same WordPress templates, for example, or a lot of the same CSS files or JavaScript files. Again, by themselves, this is not a definitive clue because there's a lot of templates out there, a lot of free stuff floating around the Internet. But when combined with the other signals, it can create a very, very clear indication of those relationships. Even something as simple as the contact details on your About Us page, if those are the same from site to site, it can be very clear that these sites are related.
Courtesy & Copyright
https://creativesaints.com/
http://graphicwebdesign.in/
https://www.papeel.com.br/
https://moz.com/blog?page=69
https://moz.com/blog/how-google-knows-what-sites-you-control-and-why-it-matters-whiteboard-friday
https://moz.com/blog?page=112
https://moz.com/blog?page=100
https://moz.com/blog?page=101