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For search engines that crawl the web, links are the streets between pages. Using sophisticated link analysis, the engines can discover how pages are related to each other and in what ways.

In 1997, Google’s founders created an algorithmic method to determine importance and popularity based on several key principles:

  • Links on the web can be interpreted as votes that are cast by the source for the target
  • All votes are, initially, considered equal
  • Over the course of executing the algorithm on a link graph, pages which receive more votes become more important
  • More important pages cast more important votes
  • The votes a page can cast are a function of that page’s importance, divided by the number of votes/links it casts

That algorithm, of course, was PageRank, and it changed the course of web search, providing tremendous value to Google’s early efforts around quality and relevancy in results. As knowledge of PageRank spread, those with a vested interest in influencing the search rankings (SEOs) found ways to leverage this information for their websites and pages.

The Value of a Link

Global Popularity

The more popular and important a site is, the more links from that site matter. A site like Wikipedia has literally 1000’s of diverse sites linking to it, which means it’s probably a popular and important site. To earn trust and authority with the engines, you’ll need the help of other link partners. The more popular, the better.

Local/Topic-Specific Popularity

The concept of “local” popularity, first pioneered by the Teoma search engine, suggests that links from sites within a topic-specific community matter more than links from general or off-topic sites. For example, your magician’s website gets more kick from a link on IBM’s magician.org site than it will from a link on an off-topic favorite pets website.

anatomy of a link

Anchor Text

One of the strongest signals the engines use in rankings is anchor text. If dozens of links point to a page with the right keywords, that page has a very good probability of ranking well for the targeted phrase in that anchor text. You can see examples of this in action with searches like “click here”, where many results rank solely due to the anchor text of inbound links.

TrustRank

It’s no surprise that the Internet contains massive amounts of spam. Some estimate as much as 60% of the web’s pages are spam. In order to weed out this irrelevant content, search engines use systems for measuring trust, many of which are based on the link graph. Earning links from highly trusted domains can result in a significant boost to this scoring metric. Universities, government websites and non-profit organizations represent examples of high-trust domains.

Link Neighborhood

Spam links often go both ways. A website that links to spam is likely spam itself, and in turn often has many spam sites linking back to it. By looking at the totality of these links in aggregate, search engines can understand the “link neighborhood” your website exists in. Thus, it’s wise to choose those sites you link to carefully and be equally selective with the sites you attempt to earn links from.

Freshness

Link signals tend to decay over time. Sites that were once popular often go stale, and eventually fail to earn new links. Thus, it’s important not only to earn links to your website, but also to continue to earn additional links over time. Commonly referred to as “FreshRank,” search engines use the freshness signals of links to judge current popularity and relevance.

Social Sharing

The last few years has seen an explosion in the amount of content shared through social services such as Facebook, Twitter and Google+. Although search engines treat socially shared links differently than other types of links, they notice them nonetheless. There is much debate among search professionals as to how exactly search engines factor social link signals into their algorithm, but there is no denying the rising importance of social channels.

Link Building Strategies

Get your customers to link to you.

link-building-strategyIf you have partners you work with regularly or loyal customers that love your brand, you can use this to your advantage by sending out partnership badges – graphic icons that link back to your site (like Google often does with their Adwords certification program). Just as you’d get customers wearing your t-shirts or sporting your bumper stickers, links are the best way to accomplish the same feat on the web.

Build a blog. Make it valuable, informative and entertaining

This content and link building strategy is so popular and valuable that it’s one of the few recommended personally by the engineers at Google. Blogs have the unique ability to contribute fresh material on a consistent basis, participate in conversations across the web, and earn listings and links from other blogs, including blogrolls and blog directories.

Create content that inspires viral sharing and natural linking

In the SEO world, we often call this “linkbait.” Such content leverages aspects of usefulness, information dissemination, or humor to create a viral effect – users who see it once want to share it with friends, and bloggers/tech-savvy webmasters who see it will often do so through links. This high quality, editorially earned votes are invaluable to building trust, authority, and rankings potential

Be newsworthy.

Earning the attention of the press, bloggers and news media is an effective, time honored way to earn links. Sometimes this is as simple as giving away something for free, releasing a great new product, or stating something controversial.

The Value of Links

Links Higher Up in HTML Code Cast More Powerful Votes

External Links are More Influential than Internal Links

Links from Unique Domains Matter More than Links from Previously Linking Sites

Links from Sites Closer to a Trusted Seed Set Pass More Value

Links from “Inside” Unique Content Pass More Value than Those from Footers/Sidebar/Navigation

Keywords in HTML Text Pass More Value than those in Alt Attributes of Linked Images

Links from More Important, Popular, Trusted Sites Pass More Value (even from less important pages)

Links Contained Within NoScript Tags Pass Lower (and Possibly No) Value

A Burst of New Links May Enable a Document to Overcome “Stronger” Competition Temporarily (or in Perpetuity)

Pages that Link to WebSpam May Devalue the Other Links they Host

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