How does Google Page Rank Work?

Submitted by alfitness

In the world of Search Engine Optimisation (SEO) there are many factors which need to taken into consideration to achieve desired outcomes. These are often categorised as either on-page or off-page factors. Things that influence on-page factors include title tags, meta descriptions and web page copy. The most significant off-page factors relate to linking and the number and quality of web pages that link to yours. Each search engine uses it's own method for determining the value and weighting of incoming links

Google uses a proprietary, trademarked algorithm called PageRank to assign a numerical value to every page of every website that it's search engine indexes. This algorithm was first published by Google's founders Larry Page and Sergey Brin in the late 90s. While the algorithm continues to be modified, the priciples at it's core remain the same. PageRank considers linking structure only when evaluating web pages. Neither site design, content or the URL are taken into consideration at all.

PageRank can be considered as a vast voting system where links are the votes. To link to a website is to effectively vote for it in Google's eyes. It's democratic - but not completely as not all links are created equal. The value of a particular link is determined by its own PageRank so for example, five links from pages with a very low PageRank might be worth less than a single link from a high ranking page.

In terms of an internal site structure, it makes sense to link all of your internal pages to one page - usually the home page as it is most likely the subject of your SEO activities and also the most visible page. While focusing on channelling PageRank to your strongest pages, it's also important to ensure that these pages not do not in turn pass their PageRank on to external pages. Google introduced the nofollow HTML attribute for just this purpose.

The nofollow attribute was also introduced to combat negative seo practices such as repeatedly posting links back to a particular website on message boards. This practice along with "black hat" SEO techniques such as link farming, keyword stuffing, hidden text and link stuffing saw a marked reduction in the relevance of search results in the mid 90s. Much of Google's success can be attributed to it's development of search algorithms like Pagerank which were able to ignore or penalise black hat techniques.

While Pagerank is a powerful and robust algorithm, it can be argued that it is limited by the fact that it favours old sites (which have had time to build/generate links) over new sites which may have better content. The other half of Google's search technology, Hypertext-Matching Analysisis designed to address this shortcoming and generate relevant search results by analysing web page content.