Keyword cannibalization isn't an issue that's in the SEO forums much, nor is it something that many SEOs feature prominently in site reviews (at least, from my experience), but it can be detrimental to potential rankings for several different reasons. First, I'll illustrate how keyword cannibalization happens.

It typically starts when a website's information architecture calls for the targeting of a single term or phrase on multiple pages of the site. Many times this is done unintentionally, but results in several or even dozens of pages that have the same keyword target in the title and header tags. I've heard several clients explain the logic behind this in a similar fashion:

Client: I want Google to know my site is about "Plaid Checkered Pants" so I made that the title of every page.
Rand: Really?...

Client: I want people to link to me with "Plaid Checkered Pants" in the anchor text, so I used that on every page.
Rand: I see...

Client: I want as many chances as possible to rank well for "Plaid Checkered Pants" so I stuffed it on every page.
Rand: Here we go again...

Here's the problem:

Googlebot Confused

Google (and the other search engines) will spider the pages on your site and see 4 (or 40) different pages on the site all seemingly relevant to one particular keyword (in this example - "snowboards"). Contrary to the belief of my three fictitious clients above, Google doesn't interpret this as meaning that your site as a whole is more relevant to "snowboards" or should rank higher than the competition. Instead, it forces Google to choose between the many versions and pick one it feels best fits the query. There's a number of rank-boosting features you lose out on when this happens:

  • Internal Anchor Text - since you're pointing to so many different pages with the same subject, you can't concentrate the value of internal anchor text on one target.
  • External Links - If 4 sites link to one page on "snowboards," 3 sites link to another of your "snowboard" pages and 6 sites link to yet another "snowboard" page, you've split up your external link value among three pages, rather than consolidating it into one.
  • Content Quality - After 3 or 4 pages of writing about the same primary topic, the value of your content is going to suffer. You want the best possible single page to attract links and referrals, not a dozen bland, replicated pages.
  • Conversion Rate - If one page is converting better than the others, it's a waste to have multiple, lower-converting versions targeting the same traffic. If you want to do conversion tracking, use a multiple-delivery testing system (either A/B or multivariate).

So what's the solution?

Googlebot finds Snowboards

The difference in this example is that instead of targeting the singular "snowboards" on every page, the pages are focused on unique, valuable variations and all of them link back to an original, canonical source for the singular term. Google can now easily identify the most relevant page for each of these queries. This isn't just valuable to the search engines; it's also a far better user experience and overall information architecture.

What should you do if you've already got a case of keyword cannibalization? Employ 301's liberally. When working with clients, I like to ID all the pages in the architecture with this issue and determine the best page to point them to, then use a 301 on every cannibalizing page to a single version. This not only ensures that visitors all arrive at the right page, but that the link equity and relevance built up over time is directing the engines to the most relevant and highest-ranking-potential page for the query.

BTW - No making fun of my robot guy. He may not be perfect, but he's the best I can do at midnight. Thanks to Cabanon Press for the robot's inspiration.