Internal website duplication has been one of the more common issues with client SEO audit reports. Websites that are prone to identical, or very close to identical, content that can be found on one or multiple pages can benefit from the new <link rel="canonical"> tag to help solve duplication problems. Here's a quick example of how this new tag works.
Let's say you have an ecommerce website with sorting capabilities for product sizes, colors, etc. The same content might appear on these three different URLs:
Now, you can simply add the <link rel="canonical"> tag to specify your preferred version such as:
<link rel="canonical" href="hxxp://www.123example.com/products/bluewidget" />. You would place this inside the <head> section of all of the duplicate content URLs, such as:
- 123example.com/products?itemid=bluewidget; and
Google will understand that the duplicates all refer to only the canonical URL: 123example.com/products/bluewidget. Further, any additional URL properties, such as PageRank and related values, are transferred as well.
Prior to this tag the only real way to ensure that internal duplication problems are not occurring within your website was to add a META noindex, nofollow or noindex, follow to possible duplicated pages.
You can read more about implementing the <link> tag at Yahoo, Google, and MSN. If you're using Drupal, WordPress, or Magento as your CMS, you can also check out Joost de Valk's page on canonical links. He has included a plugin or module to add the <links> tag within your Drupal, WP, or Magento website.