Why are links important for SEO?

Why are links important for SEO?

Links are important because they are a good metric for representing how valuable a website is.
Compared to other metrics such as traffic, which is often kept private, links are a publicly visible way of gauging how popular or important a website is.

In very basic terms, a link can be seen as a vote.
The more votes you get, the higher you rank in Google.

Whilst that serves as a nice analogy, the truth is a little more complex.

Unlike in a democratic vote in which all votes carry equal weight, in the Google algorithm; All links are equal, but some are more equal than others.

For example a link from:

Viagra site

is worth significantly less than a link from


Something worth remembering is that the web still remains something like the wild west.
You can see this in many ways, from Anonymous, to the Pirate Bay, Super-Injunctions, Governments desperately trying to bring law and order to the web, etc.


The internet remains a relatively lawless place where Governments struggle to impose order.

The internet remains largely unpoliced and remains a place where men or women with dubious morals can earn a fast buck or two.
In terms of SEO, Google acts like the chief sheriff in town.

But why is this?
Firstly we need to think what Google takes into account when evaluating a link source.
There are many things but some classic examples include things like:

Domain Age:
Number of Backlinks
C-Class Pop
Dom Pop
Domain Authority
Trust Rank
to a lesser extent, PR

If we start with Domain Age. The older a domain is the better, since a website that has been around for some time shows that it theoretically has some value that trustworthiness. A domain that is 10-15 years old is far less likely to be a spammy website, since spamming tends to burn out a domain very quickly leading the spammer to move on to a new domain.
Also Domain age is very hard to fake. (impossible to fake) but you can buy old domains.

The number of backlinks is pretty self explanatory ;)

C-Class and Dom Pop.
These are perhaps the most important figures in terms of calculating the importance of a link source. If I could only take 1 metric to evaluate a link source, then it would certainly be C-Class Pop.

Dom Pop and C-Class Pop are figures that are derived from the overall number of links that a site has.
For example:

A site has 1000 backlinks.
Those 1000 backlinks come from 500 Different Domains.
For example, if each website gave 2 links to our website then we would have 1000 links in total, from 500 different websites :)

To understand C-Class pop, we need to first establish what C-Class means.
C-Class relates to the server, or cluster of servers, on which a website is hosted.
So if you choose website hosting from a company and then host 10 websites with them, there is a very high chance that all of your websites will be hosted on the same server or server cluster and have the same C-Class id.

Why this is important is it prevents people buying hundreds/thousands of domains, hosting them on a cheap/free host, and pointing links from them to their main website.

If I bought a 1000 domains, set them up on a free host and linked them all back to my target site. I might end up with figures like:

5000 Links
1000 Dom Pop

Which looks quite good!

until we see: C-class pop: 1

this obviously looks unnatural and Google would be asking if it is reasonably possible for a website to get such a backlink profile.

Trustrank is a way of gauging how trusted a website is by gauging how well linked it is from trusted websites such as websites ending in .gov or .edu. These are seen as trusted sources and, by implication, only link to other websites that are trustworthy and respectable.
The more links you have from authority pages, the stronger your trust rank.
It’s also worth noting that this metric is calculated a little like the 6 degrees of separation so if an authority page links to a site that in turn links to you, then you receive some diluted trust via this connection :)

Domain Authority
Domain Authority is a nice little handle to put on how trusted and important a website is, it draws on figures such as Trustrank and backlink profile to build a nice overall metric with which you can begin to gauge a sites authority.

Page Rank.
Whilst PR was perhaps the main metric by which one would judge a link source historically, due to abuse by SEO's and the ease at which it can be manipulated, PR is no longer seen as the poster child of link source appraisal.

By taking all of these metrics into account, we can build up a decent idea of how important a website is as a link source.

Anchor text relevancy
What is also important in terms of backlinks is the text that is chosen as the anchor text.
This means the clickable part of the link, often things like "click here" or "See More" etc.

The reason this is important is that it shows Google.
I am linking to this URL and the word/phrase that I am choosing to link here with is this "…"
Therefore, by implication, this website I am linking to is related to the word I choose to use.

If I choose to link to a Wikipedia Article about the Titanic, it's probable that I would choose to link with the word "Titanic" as this is a relevant word to use.
With this in mind, Google draws keyword relevancy from the link text of external (and internal) links.
The more links that use the selected keywords, or derivations thereof, the greater the extent of the keyword relevancy that Google assigns.

As with all things SEO, there are some clowns that spoil the party. Remember how we said early on that the web remains like the wild west and that SEO's abuse everything they get their hands on?
Well the same is true here, if you look at horribly spammy links on spammed blogs or forums you will see lots of them with anchor texts like "buy cheap Viagra" "cheapest Nike shoes" etc.
As with all things SEO, moderation and temperance should prevail.

Link Spam.

So, since we have established that links are like votes, and that SEO's ruthlessly exploit and abuse the wild west web, spamming links to places is a big problem. Anyone that has

forum link spam

An example of forum link spam.

their own blog or website will be aware of the deluge of spam link comments that they receive on a daily basis.
This got progressively worse in the early part of the last decade as ruthless spammers would bombard websites with a barrage of spam comments in the hope that some would get through and provide the all important backlink they were seeking.

This became more and more of a problem for website owners, who would be forced to either ban all links, or sift through them all manually, picking out the spam.

Webmasters became pretty angry, and seeing that this was a problem that Google had created, they began to call on Google to find a solution to the problem.

Google responded to the calls of webmasters and on the 18th of Jan, 2005 they announced something that would change linkbuilding forever.

If you’re a blogger (or a blog reader), you’re painfully familiar with people who try to raise their own websites’ search engine rankings by submitting linked blog comments like “Visit my discount pharmaceuticals site.”
This is called comment spam, we don’t like it either, and we’ve been testing a new tag that blocks it. From now on, when Google sees the attribute (rel=”nofollow”) on hyperlinks, those links won’t get any credit when we rank websites in our search results. This isn’t a negative vote for the site where the comment was posted; it’s just a way to make sure that spammers get no benefit from abusing public areas like blog comments, trackbacks, and referrer lists.


A small revolution.

At just 15 characters long, the rel="nofollow" tag sought to prevent link spam in one fell swoop.
And to some extent it has worked, but not to the point where it has eliminated link spam entirely.
What the nofollow tag does is tell Google "this is a link but NOT a vote"
The link passes no power or authority to the target site.
In terms of linkbuilding there is very little to be gained by building nofollow links.

Now, for any of these links to count in terms of SEO, we need to be sure that Google is both able to see them and knows they exist.

This comes down to a question of Crawlability and Indexing.

In order to count a link, Google must be able to access the page on which the link is placed.
Important things to remember here are the check that the page is not only accessable to logged in users, or blocked by some other method.
an easy way to check this is to see if the page is in the Google cache.
in chrome you can simply type "cache:" at the beginning of a URL.

If the page is cached, this means Google can crawl it.

It might be that the page is set as "noindex" now it would be wrong for me to say that any page that is set as noindex can't be seen by Google, but it's a little complicated and my best advice would be to avoid them unless specifically told otherwise ;)

Aaaaand Finally.

Link Placement.
Here is a another example where all links are not equal.
Since, again, SEO's abuse and exploit any weakness they perceive in the Google algorithm.
In the latter half of the last decade, the idea of sticking links in the footer of a website or in the sidebar became popular. It was possible for website owners to sell or rent link space in the footer of their websites or in the sidebar. Since this was very easy and quick for the webmaster to implement and the sponsoring website got a nice link to the page they were looking to promote.
In the example here we have a bunch of links in the footer, made worse by the fact that they are almost the same colour as the background. Really shitty SEO trickery.

Footer Links Example

An example of bad footer links

We have to think.
Are these links presenting any benefit for the website user? Or are they there simply for SEO?

In this case I think it is clear to see that the links here are certainly not for the user benefit.
Google identifies this and looks less than favourably upon it.

The ultimate link is what we call a "contextual-link" one that is in the text of the body and forms part of the article.
Which bring me on to a great point to finish on.

In terms of SEO, you should not be thinking "what does Google want me to do", rather "What presents the best experience for my users"

Google tells us "don’t build websites for search engines, build websites for people"

Putting blue on blue links in the footer, spamming blog comments with nonsense, engaging in dubious link swaps and link schemes, ultimately isn’t going to to get you very far in the long run. Whilst you might make some small gains in the short term, you will fall in the long run. Google is smart and getting smarter every day, they make over 400 algorithmic changes each year.
If you want to build links in the shady and bad way, just remember you are playing cat and mouse with Google, on their turf, in a game they created, and for which they make the rules.