Rand of SEOmoz.org posted an interesting article on duplicate content issues. He uses the typical blog to show different examples.
In a blog, every post can appear in the home page, pagination, archives, feeds, etc.
Rand suggests the use of the meta robots tag “no-index”, or the potentially risky use of cloaking, to redirect the robots to the original source.
Joost the Valk recommends WordPress users change some lines in the source code to address these problems.
There are a few items I would like to add to the problem and to the proposed solution.
As willcritchlow asks, there is also the problem of multiple URLs leading to the same content (ie.: www.site.com, site.com, site.com/index.html, etc.). This can be fixed by using HTTP redirects and by telling Google what is our preferred domain via webmaster central.
Reader roadies, recalls reading about a robots.txt and .htaccess solution somewhere. That gave me the inspiration to write this post.
After carefully reviewing Google’s official response to the duplicate content issue, it occurred to me that the problem might not be as bad as we think.
What does Google do about it?
During our crawling and when serving search results, we try hard to index and show pages with distinct information. This filtering means, for instance, that if your site has articles in “regular” and “printer” versions and neither set is blocked in robots.txt or via a noindex meta tag, we’ll choose one version to list. In the rare cases in which we perceive that duplicate content may be shown with intent to manipulate our rankings and deceive our users, we’ll also make appropriate adjustments in the indexing and ranking of the sites involved. However, we prefer to focus on filtering — rather than ranking adjustments … so in the vast majority of cases, the worst thing that’ll befall webmasters is to see the “less desired” version of a page shown in our index.
Basically, Google says that unless we are trying to do something purposely ill intended (like ‘borrowing’ content from other sites), they will only toss out duplicate pages. They explain that their algorithm automatically detects the ‘right’ page and uses that to return results.
The problem is that we might not want Google to choose the ‘right’ page for us. Maybe they are choosing the printer-friendly page and we want them to choose the page that includes our sponsors’ ads! That is one of the main reasons, in my opinion, to address the duplicate content issue. Another thing is that those tossed out pages will likely end up in the infamous supplemental index. Nobody wants them there :-).
One important addition to Rand’s article is the use of robots.txt to address the issue. One advantage, this has over the use of the meta robots tag “no-index”, is in the case of RSS feeds. Web robots index them, they contain duplicate content but the meta tag is intended for HTML/XHTML content and the feeds are XML content.
If you read my post on John Chow’s robots.txt file, you probably noticed that some of the changes he did to his file, were precisely to address duplicate content issues.
Now, let me explain how you can address duplicate content via robots.txt. Read more