Friday, 20 February 2009

Canonical Links and Content Duplication

For a long time now, search engines have been implementing stringent measures to stop website owners manipulating rankings through content duplication. The way the Internet has evolved over the recent years however, has meant that some sites have been running the risk of being unfairly penalised for content duplication caused more by the technology they are using rather than their intent.

In an effort to address this, the big three (Google, Yahoo, MSN) decided last week to support a common standard which aims to eradicate duplicate URLs within a site.

Image representing Google as depicted in Crunc...Image via CrunchBase

The standard being introduced is very simple, and consists of no more than nominating a single URL (or "canonical" location if you're a search engine) and defining this on all other URLs where the same content is replicated.

Take the following URLs as an example:

These three URLs will display exactly the same content even though the page has three very distinct URL locations based on the origin of the visit and its optimisation.

The agreed standard requires no more than the following syntax being implemented within the <HEAD> section of the two dynamic URLs.

<link href="" rel="canonical"/>

Doing this, will make search engines aware of the preferred URL and pass on any PageRank and link equity the dynamic URLs may have gained across to the chosen URL.

Google guru Matt Cutts explains Canonical Linking on an interview for WebProNews. You can also find out more directly from Google, Yahoo, and MSN.

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