Best way to implement canonical tags on an ecommerce site with many filter options?

[DA2013]

What would be the best way to add canonical tags to an ecommerce site with many filter options, for example, http://teacherexpress.scholastic.com?

Should I include a canonical tag for all filter options under a category even though the pages don't have the same content?

Thanks for reading!

[FedeEinhorn]

Hey Daniel,

The canonical should point on every possible filtering to the main page without any filter.

Check the following Q&A from Yesterday: http://moz.com/community/q/canonicalization-w-search-and-filter-operators-parameters

Hope that helps.

[DA2013]

Thank you very much Federico!

I saw a couple of articles warning against canonicalizing if the content isn't extremely similar. Can you help me understand how this doesn't apply?

e.g. Searchenginewatch: "The most common misuse of the tag is when it's implemented on pages that don't include a large percentage of the same content as the canonical page. Unless they contain considerable chunk of duplicate content, rel="canonical" probably shouldn't be used."

Google:

Must the content on a set of pages be similar to the content on the canonical version?

Yes. The rel="canonical" attribute should be used only to specify the preferred version of many pages with identical content (although minor differences, such as sort order, are okay).

For instance, if a site has a set of pages for the same model of dance shoe, each varying only by the color of the shoe pictured, it may make sense to set the page highlighting the most popular color as the canonical version so that Google may be more likely to show that page in search results. However, rel="canonical" would not be appropriate if that same site simply wanted a gel insole page to rank higher than the shoe page.

[Dr-Pete]

This is generally an exception Google supports - for example, they say that you can use rel=prev/next and rel=canonical in conjunction, where one handles pagination and the other handles sorts/filters. In the case of a sort (like ascending/descending) the actual results could be very different, but the intent is still legitimate. They generally understand you're trying to clean up these pages.

In a perfect world, these filters wouldn't create unique URLs, honestly, but now that they already exist, you have to manage them. The other option would just be to META NOINDEX those filter URLs or set them up in parameter handling in Google Webmaster Tools. I tend to prefer the canonical here, personally.