Domain-Level Link Features
(e.g. quantity of links to the domain, trust/quality of links to the domain, domain-level PageRank, etc.)

Page-Level Link Features
(e.g. PageRank, TrustRank, quantity of link links, anchor text distribution, quality of link sources, etc.)

Page-Level KW & Content Features
(e.g. TF*IDF, topic-modeling scores, on content, content quantity/relevance, etc.)

Page-Level, Keyword-Agnostic Features
(e.g. content length, readability, uniquness, load speed, etc.)

Domain-Level Brand Features
(e.g. offline usage of brand/domain name, mentions of brand/domain in news/media/press, entity association, etc.)

User, Usage, & Traffic Query Data
(e.g. traffic/usage signals from browsers/toolbars/clickstream, quantity/diversity/CTR of queries, etc.)

Social Metrics
(e.g. quantity/quality of tweeted links, Facebook shares, Google +1s, etc.)

Domain-Level Keyword Usage
(e.g. exact match keyword domains, partial-keyword matches, etc.)

Domain-Level, Keyword-Agnostic Features
(e.g. domain name length, extension, domain HTTP response time, etc.)
It is generally accepted that if all other factors are equal, the volume and quality of links pointing to a page will make the difference between rankings. Having said that, with recent moves from Google, including the release of Penguin updates and its push of Google+, there is speculation that the impact of links is being reduced and replaced with social signals such as tweets or +1s.

For now, though, there is little doubt that if you get high-quality links to your website, it will help you rank better and get more traffic (we’ll talk more about what makes a “good-quality” link in Chapter 2). We’ve mentioned “high-quality” a few times, now, and there’s a good reason: The focus on quality is increasing as Google becomes ever more sophisticated at filtering out low-quality links. This directly impacts SEOs, as they need to make sure the link building techniques they choose focus primarily on that quality.