What we should know about PageRank
Google's PageRank is an algorithm and a value to measure the popularity and the relevance of a page on the Web. It is a leading indicator of the ranking in search results.
A legend spread by webmasters who have a very partial understanding of how search engine work argues that "PageRank is dead."
This is not the case and it will never be the case. While innovative search engines like Wolfram Alpha have a completely different back-end, however they represent a tiny fraction of web searches, and they provide content pages they produce, not lists of external pages and they did not deal with spam. PageRank is still needed to assess the value of a page.
- The name PageRank is a registered trademark.
It was originally a pun on the word page and the name of one of the two Google founders, Larry Page.
- The success of Google was born out of the use of the PageRank algorithm.
By which ranks sites according to links and not on the number of keywords in the page as did the search engine AltaVista (few Internet still know AltaVista).
- The pages are crawled in order of PageRank.
The pages that have the highest PR are scanned more often and more completely. Linked pages will be too, but the most we follow links and the the most keeping track fades.
(Ref. Matt Cutts).
- PageRank is an index reflecting the proportion in number and importance of links on a page.
- The PR of a page is sent to linked pages.
But the value passed corresponds to the PR of the page divided by the number of links on the page. As shown in the graph on the right.
(Ref SEO for bloggers).
- The nofollow attribute in a link does not pass the PR to the page that is linked.
But its share of undistributed PR is not assigned to other links, it is lost. See PageRank and nofollow.
- The PageRank contributes to the ranking of a page in Google results.
But it is a signal among many others. See the main factors for ranking.
- The increase in PageRank has a progressive difficulty.
It does not depend linearly on the importance of backlinks but logarithmically. So when we progress continuously, it takes much more time to go from 4 to 5 than from 3 to 4.
- Several links in a page have no more value than one.
A page with several links to another same page does not transmit more PR than with one. Only the first is taken into account, in addition, if the anchors differ, it is the anchor of the first link that is taken into account to assign keywords to the target.
- All pages are equal.
The algorithm does not distinguish the index page or pages at the root of the site and deep pages. He distinguishes "Landing pages", those that are popular and have the most backlinks and others. Popular pages transmit PR and traffic to others. Internal links should be studied according to this.
- A 301 redirect means losing some PageRank
When a page is redirected by a 301 HTTP code, the new page does not keep the full PageRank, it is dininushed by a small factor. As a result, the new page could lose its ranking. This was confirmed by Matt Cutts (an has been verified in live).