Duplicate Content has long been an issue with webmasters and is cause for concern because duplicating content dilutes your ranking in search results. Perhaps the most common cause of having duplicate content is in allowing both www. and non www versions of your site to exist. However, another place where I see duplicate content occur is when a customer has multiple domain names pointing to the same content. When you use multiple domain names, and there are good reasons to do this, you should pick a preferred URL and ensure that any secondary domains are 301 redirected to that URL.

In this video, Google’s Greg Grothaus does a great job explaining duplicate content problems and solutions ranging from 301 redirects to canonical tags.

I have previously blogged about how 301 redirects can prevent common problems from diluting the search engine ranking for your site. However, there are however a number of situations that create duplicate content concerns that are more difficult address. Webmasters now have additional tools to deal with duplicate content through Google’s Webmaster Tools panel. Through this addition to webmaster tools, Google Lets You Tell Them Which URL Parameters To Ignore. This will a great help, especially for many large dynamic sites.

SEO 301 redirects, Canonical, duplicate content, Linking, SEO, spidering, www

There is a new Canonical tag that is supported by Google, Yahoo, and Microsoft. This is important news, especially as people are working more and more with CMS systems and database driven websites (such as Joomla, WordPress, etc).

The issue is that people can arrive at your content in a variety of ways. The simplest variation being www. versus non www. version of your site. What’s that, you say they are the same?  Au contraire mon fraire, to a search engine www is a separate sub-domain. There are some easy programmatic ways to address the www versus non www  issue, however the problem starts to get sticky in when you mix in the wide range of variables such as dates, tags, and categories that can be included in the URL structure.

The search engine spider may find variations like these all pointing to the same content:

• www.mywebsite.com/january 2009/search-engine-optimization
• www.mywebsite.com/seo-tag/serach-engine-optimization
• www.mywebsite.com/author-allen/serach-engine-optimization

 Worst still are session ids (used on larger sites) which can cause a single page of content to be indexed hundreds of times:

• www.mywebsite.com/serach-engine-optimization/sessionid=123

Add to this that you can’t control how others link to your content and you begin to understand why duplicate content is such a large issue.  

Why should you care? From and SEO perspective 1 page with 100 incoming links has far more relavency than 100 pages with identical content having one incoming link each. 

To address these concerns, Google, Microsoft and Yahoo have agreed to take the content of the Canonical Link Tag as the preferred name for a page.

So adding a tag such as:
<link rel=”canonical” href=”http://www.mywebsite.com/serach-engine-optimization“/>
will indicate that the page should be indexed as www.mywebsite.com/serach-engine-optimization, regardless of how the spider found the page.

Here’s a link to more information on this topic by Vanessa Fox  at Search Engine Land:
http://searchengineland.com/canonical-tag-16537 

Google’s Matt Cutts posted this video on the Canonical Link tag.
http://google.com/support/webmasters/bin/answer.py?answer=139394

The discussion begins hitting of some of the finer points of this topic starting in at about 12:05.

SEO Canonical, google, incoming links, microsoft, SEO, Yahoo