1.Number of links
Google’s ranking algorithm takes into account the number of domains and pages that link to a website. Various studies show strong correlation between the number of backlinks and rankings.
Here’s an extract from Larry Page’s presentation of Google search:
“…counting citations or backlinks to a given page… gives some approximation of a page’s importance or quality. PageRank extends this idea by not counting links from all pages equally, and by normalizing by the number of links on a page.”
Definitely, backlinks are one of the most important ranking factors and the number of backlinks matters. However, backlinks are not treated equally, and quality mostly trumps quantity. Thus, you need to strive for getting backlinks from quality an authoritative websites, rather than chasing big numbers.
2.Links from relevant sources
Backlinks from the sources relevant to the referred page are considered to be strong ranking signals.
Google’s Webmaster Central Blog stressed the value of relevant links, saying:
“We continued to protect the value of authoritative and relevant links as an important ranking signal for search.“
Here’s another mention, from an earlier post:
“As many of you know, relevant, quality inbound links can affect your PageRank (one of many factors in our ranking algorithm).“
It’s quite obvious that Google considers backlinks from topically relevant websites or pages as strong ranking signals. So again, a couple of backlinks from relevant websites (of the same niche) or pages with topically relevant content may do you much more good than a ten of links from less relevant sources.
3.Backlinks anchor text
Anchor texts of backlinks may signalize of a linked page relevance and thus, impact rankings of the page for target keywords.
The initial Google search engine algorithm description explains how anchor texts are treated.
“The text of links is treated in a special way in our search engine.
…we associate it with the page the link points to. This has several advantages. …anchors often provide more accurate descriptions of web pages than the pages themselves.”
However, Google warns against unnatural optimized anchors.
“Here are a few common examples of unnatural links that may violate our guidelines:
…Links with optimized anchor text in articles or press releases distributed on other sites. For example: There are many wedding rings on the market. If you want to have a wedding, you will have to pick the best ring.”
Well, this looks like a delicate topic, because you really need to be cautious with keyword-based anchors. On the one hand, search algorithm takes into account anchor texts. On the other hand, excessive use of keyword-based anchors may look unnatural and, consequently, suspicious and do more harm than good in the final count. So it’s highly advisable to use keyword-based anchors reasonably. Think of anchor texts as short descriptions of the content you link to, and avoid stuffing them with target keywords.
4.Links from .edu/ .gov domains
Backlinks from .edu and .gov domains are considered to pass more weight to websites they refer to.
Google’s Matt Cutts stated that links form .edu and.gov domains are normally treated just like any other backlinks.
“It’s not like a link from an .edu automatically carries more weight, or a link from a gov automatically carries more weight.”
John Mueller went even further and claimed that they have been ignoring a lot of .edu links.
“Because of the misconception that .edu links are more valuable, these sites get link-spammed quite a bit, and because of that, we ignore a ton of the links on those sites.”
Domains like .edu and .gov are at large quality, authoritative websites, so they usually get higher ranks. However, when it comes to passing on their weight, Google tends to treat them equally to other websites, not putting any additional weight on them just for having such domain extensions. Instead of putting efforts into earning a link from a .gov site, for example, it’s much wiser to try and earn links from niche relevant sites.
Though outbound links are supposed to leak your pages weight, linking to quality, authoritative resources may work in favor of your rankings.
Here’s what John Muller told about outbound links back in 2016:
“Our point of view… links from your site to other people’s sites isn’t specifically a ranking factor. But it can bring value to your content and that in turn can be relevant for us in search.”
Here’s how he answered about the impact of outbound links on SEO in a recent Hangouts session:
“Linking to other websites is a great way to provide value to your users. Often times, links help users to find out more, to check out your sources and to better understand how your content is relevant to the questions that they have.”
Well, there is neither definite ‘yes’ nor definite ‘no’. It seems that outbound links look fine to Google, as they are, put in the relevant context, helping users to examine the subject they are interested in more comprehensively.
A stable, continuous growth of the number of backlinks over time speaks of a website’s increasing (or continuing) popularity, so it may lead to higher positions in search results. If a website is losing more links than acquiring over time, Google demotes its positions.
One of the Google’s patents dwells on scoring websites based on links behavior. Here are some extracts:
“…the link-based factors may relate to the dates that new links appear to a document and that existing links disappear.”
“Using the time-varying behavior of links to (and/or from) a document, search engine may score the document accordingly.”
I think, it is likely that Google determines when websites gain and lose backlinks. By analyzing this data it can make assumptions on their growing or falling popularity and treat the websites accordingly — promote or demote them in the SERPs. So if your page continues to get backlinks over time, it may be considered relevant and ‘fresh’, and may be eligible to higher ranks.
7.Links through 301 redirects lose some weight
Links pointing to a redirected page pass less weight to a destination page than direct links to that page. So, 301 redirects work somehow like a negative ranking factor.
Back in 2016, Garry Illyes clarified this matter, saying “30x redirects don’t lose PageRank anymore”.
Later on, answering a question about link equity loss from redirect chains, John Mueller claimed the following:
“For the most part that is not a problem. We can forward PageRank through 301 and 302 redirects. Essentially what happens there is we use these redirects to pick a canonical. By picking a canonical we’re concentrating all the signals that go to those URLs to the canonical URL.”
At the end of the day, there’s no difference for Google between a direct link and a link that points to a redirected page. The latter will pass the same weight to the destination page, as if it was a direct link. So it’s likely that you don’t need to fret too much about 301 redirects. However, too many redirects (and redirect chains) can have a bad impact of website’s performance (and performance IS a ranking factor). What’s more, the excessive number of redirects is bad for site’s crawl budget.
Google’s ranking algorithm doesn’t take into account links marked with a nofollow attribute. Such links don’t carry any weight, thus you can’t count on them (in terms of having any ranking impact).
Recently, Google has announced a new approach
to counting nofollow links, saying they would treat them not as directives, but hints.
“When nofollow was introduced, Google would not count any link marked this way as a signal to use within our search algorithms. This has now changed.See more about SEO.
All the link attributes — sponsored, UGC and nofollow — are treated as hints about which links to consider or exclude within Search.”
Another piece of info comes from Gary Illyes, saying:
“The move to a hint based system may cover every link list to nofollow, including those from publications that blanket nofollow. We don’t however have anything to announce at the moment, but I’m sure your sites will appreciate this move on the long run.”
The nofollow attribute was introduced to fight the spammy links some 15 years ago. It was serving as an instruction for search engine bots not to take this link into account. From now on, it will be up to Google to decide whether to use the link for ranking purposes or not. It’s unclear, however, what would influence the decision.