Link dilution from too many links on one page?

Discussion in 'Link Development' started by MarketExpert, Mar 6, 2009.

  1. #1
    Is there such a thing?
     
    MarketExpert, Mar 6, 2009 IP
  2. Canonical

    Canonical Well-Known Member

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    #2
    First of all I wouldn't say page, I would say URL. Google and the other engines index URLs, not pages. Every unique URL is considered a different 'page' in their eyes, at least until recently when they Google, Yahoo, and MSN announced the support for <link rel="canonical">.

    To answer the question... Yes! The more oubound links a page has, the less Page Rank (or link juice) gets passed out to each of the target pages.

    Here is the original description of Page Rank by Larry Page and Sergey Brin when they conceived Google at Stanford documented in a paper called The Anatomy of a Large Scale Hypertextual Web Search Engine. Once you understand the formula, you can see how Page Rank is based on the inbound links of the page and that the more outbound links a page has, the less PR it passes the links:

    2.1 PageRank: Bringing Order to the Web

    The citation (link) graph of the web is an important resource that has largely gone unused in existing
    web search engines. We have created maps containing as many as 518 million of these hyperlinks, a
    significant sample of the total. These maps allow rapid calculation of a web page’s "PageRank", an
    objective measure of its citation importance that corresponds well with people’s subjective idea of
    importance. Because of this correspondence, PageRank is an excellent way to prioritize the results of
    web keyword searches. For most popular subjects, a simple text matching search that is restricted to web
    page titles performs admirably when PageRank prioritizes the results (demo available at
    google.stanford.edu). For the type of full text searches in the main Google system, PageRank also helps
    a great deal.

    2.1.1 Description of PageRank Calculation

    Academic citation literature has been applied to the web, largely by counting citations or backlinks to a
    given page. This 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.
    PageRank is defined as follows:

    We assume page A has pages T1...Tn which point to it (i.e., are citations). The parameter d
    is a damping factor which can be set between 0 and 1. We usually set d to 0.85. There are
    more details about d in the next section. Also C(A) is defined as the number of links going
    out of page A. The PageRank of a page A is given as follows:

    PR(A) = (1-d) + d (PR(T1)/C(T1) + ... + PR(Tn)/C(Tn))

    Note that the PageRanks form a probability distribution over web pages, so the sum of all
    web pages’ PageRanks will be one.

    PageRank or PR(A) can be calculated using a simple iterative algorithm, and corresponds to the
    principal eigenvector of the normalized link matrix of the web. Also, a PageRank for 26 million web
    pages can be computed in a few hours on a medium size workstation. There are many other details
    which are beyond the scope of this paper.
     
    Canonical, Mar 6, 2009 IP
  3. falguni1

    falguni1 Peon

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    #3
    wow good info thanks.

    What is the meaning of <link rel="canonical">
     
    falguni1, Mar 6, 2009 IP
  4. Canonical

    Canonical Well-Known Member

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    #4
    You should have one and only one URL to refer to a particular page. This is called the canonical URL. In the past canonical URLs were achieved using 301 Permanently Moved redirects.

    For example, if your home page is named index.html, there are lots of URLs that might be used to reference it:

    example(dot)com
    example(dot)com/
    example(dot)com/index.html
    www(dot)example(dot)com
    www(dot)example(dot)com/
    www(dot)example(dot)com/index.html

    If each of the above URLs had 10 inbound links Google and the other search engines would consider them 6 separate pages each with 10 inbound links.

    To correct this you would decide on rules to create canonical URLs and enforce them site-wide using 301 redirects. Typically you decide on things like:

    1) www or non-www
    2) show trailing '/' on folders with default documents (like index.html) or hide the trailing '/'
    3) show default document name on folders with default documents or hide the default document name

    I always go with www, show trailing '/', and hide default document names. So my home pages are always of the form www(dot)example(dot)com/.

    So to implement the canonical URL www(dot)example(dot)com/ I would redirect as follows:

    example(dot)com ---> 301 Redirect to ---> www(dot)example(dot)com/
    example(dot)com/ ---> 301 Redirect to ---> www(dot)example(dot)com/
    example(dot)com/index.html ---> 301 Redirect to ---> www(dot)example(dot)com/
    www(dot)example(dot)com ---> 301 Redirect to ---> www(dot)example(dot)com/
    www(dot)example(dot)com/ --- Canonical URL - No Redirect
    www(dot)example(dot)com/index.html ---> 301 Redirect to ---> www(dot)example(dot)com/

    The 301 redirects tell Google 1) to replace the old URL with the new URL in their index and 2) to give the new URL credit for all of the old URL's inbound links and link text. So Google now sees this as 1 page with 60 inbound links and all 60 link texts used to link to the page.


    A couple of weeks ago, Google, Yahoo! and MSN agreed to start supporting a new syntax for the <link> element. It is of the form <link rel="canonical" href="yourcanonicalURL">.

    If you include <link rel="canonical" href="/"> in the <head> of the index.html, no matter which of the above URLs are used to request your home page, the www(dot)example(dot)com/ canonical URL would be given credit for the inbound links for all of the 6 URLs, eliminating the need for 301 redirects to achieve canonicalization.
     
    Canonical, Mar 6, 2009 IP
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  5. Canonical

    Canonical Well-Known Member

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    #5
    PS: Sorry about the (dot) notation. And all of the above URLs should also have "http"+"://" in front of them... But being as I'm a new poster, I cannot imbed any type of URL... *** sigh ***
     
    Canonical, Mar 6, 2009 IP
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  6. MarketExpert

    MarketExpert Well-Known Member

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    #6
    Thanks, You may vary well be correct.
     
    MarketExpert, Mar 7, 2009 IP
  7. MarketExpert

    MarketExpert Well-Known Member

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    #7
    As a new poster you have done very well.
     
    MarketExpert, Mar 7, 2009 IP
  8. Canonical

    Canonical Well-Known Member

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    #8
    Thanks... I'm new to this forum... but not to SEO. :)
     
    Canonical, Mar 7, 2009 IP
  9. JJMTB

    JJMTB Peon

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    #9
    good info thanks
     
    JJMTB, Mar 8, 2009 IP
  10. rena

    rena Peon

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    #10
    Useful thread and appreciate all for it
     
    rena, Mar 8, 2009 IP
  11. greenpinion

    greenpinion Peon

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    #11
    Thanks, this is useful.
     
    greenpinion, Mar 8, 2009 IP