link-value
  • External links:
    • What others say about you is more important than what you say about yourself.
    • External links carry more weight than internal pages links.
  • Anchor text:
    • It is the biggest factor in ranking equation.
    • Exact match anchor text is more beneficial than simple inclusion of keywords in an anchor text phrase. 
  • Page Rank:
    • StaticRank, WebRank, PageRank, MozRank are various names but every Engine uses a similar Markov-chain link analysis algorithm for ranking system.
    • Refer: The professional Guide to PageRank optimization for details.
    • Every URL is assigned an innate quantity of PageRank. If there are “n” links on a page, each link passes that page’s PageRank divided by “n”
    • Representations are on  0-10 logarithmic scale (Page-Rank: 4 has 8-10Xlink importance than  PR 3)
    • Domain Rank can be calculated based on domain level links graph.
  • Trust Rank:
    • Refer for basics: Combatting Webspam with Trust-Rank (pdf).
    • Used to predicatively state whether a site/page is likely to be high quality or a spam.
    • Trust-Rank (and Reverse Trust-Rank) can be calculated on both the page-level and domain-level link graph.
    • Try getting links from high trust sites and not the potential spam ones.
  • Domain Authority:
    • Combination of popularity, importance, trustworthiness and age is calculated by the search engines based largely on link data.
    • Search engines count the links to calculate Domain Authority.
  • Diversity of Sources:
    • Calculated by the number of linking root domains.
    • Find list of top pages and top domains on the web ordered by the number of unique root domains.
    • Links from new domains are more valuables than new links from domains already linking in
  • Uniqueness of Source + Target:
    • Number of shared, reciprocated links.
    • Domain registration data.
    • Shared hosting IP address or IP address C-blocks.
    • Public acquisition/relationship information.
    • Machine-readable and interpretable Publicized marketing agreements.
    • Anecdotal evidence that links shared between “networks” of websites pass little value (site-wide links)
  • Content & Context Assessment:
    • Engines discern, in a machine parse-able way, why a link exists on a page and the context of it with the content.
  • Geographic Location:
    • Engines pinpoint the location-relevance of a root domain, sub-domain or subfolder.
    • Various ways are host IP address, country-code TLD extension, content language; local search systems Registration, physical address Associations etc.
  • Use of Rel=”Nofollow”:
    • rel=”nofollow“, when attached to a link, tells the engines not to ascribe any editorial endorsements or “votes” that would boost a page/site’s query independent ranking metrics.
  • Link Type:
    • Types are Straight HTML Text Links, Image Links, Java-script Links.
    • Not all links are treated equally. HTML links (standard anchor text) pass the most value, than image links (keyword-rich alt text) and finally, Java-script (which still aren’t universally followed as an endorsement).
  • Other Link Targets on the Source Page:
    • Link from a page that also links to low quality pages/ spam is less valuable than links from pages that link to high quality domains/ URLs.
  • Domain, Page & Link-Specific Penalties:
    • Engines apply penalties to sites/pages ranging from the loss of the ability to pass link juice/endorsement all the way up to a full ban from their indices
    • Search Engines show penalties publicly (inability to rank for obvious title/URL matches, lowered PageRank scores, etc.) but continue to keep these penalties inconsistent so systemic manipulators can’t acquire solid data points about who can gets “hit” vs. not
  • Content/Embed Patterns:
    • Content licensing & distribution, widgets, badges and distributed, embeddable links-in-content are stopped by engines.
  • Temporal / Historical Data:
    • Search Engines use patterns (about how new sites, new pages and old stalwarts earn links) data to help fight spam, identify authority and relevance and even deliver greater freshness for pages that are rising quickly in link acquisition.