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Question: We have seen some debate on various other Joomla SEO blogs about Joomla Google and duplicate content penalties. Some say there is a problem. Others say there isn't. What is your take?

Answer: Good question. For the newbie, let's first detail the problem. The exact issue is this.  Joomla, because of its architecture creates multiple URLS for the same content item.  It all depends on how the content item is navigated to.

We have claimed in the past that this is problem called "duplicate content" and Google may see it as spam.  Some people claim Google says this is NOT a problem and so ignore it.  Others claim that it is more of a Page Rank dilution problem.

These statements from Googles webmaster guidelines and blog are what cause the contradictory opinons.

"Don't create multiple pages, subdomains, or domains with substantially duplicate content."

Google also says,

"When we detect duplicate content, such as through variations caused by URL parameters, we group the duplicate URLs into one cluster.

We select what we think is the "best" URL to represent the cluster in search results.

We then consolidate properties of the URLs in the cluster, such as link popularity, to the representative URL.

Google also states:

"...Google's idea of what the "best" URL is might not be the same as your idea. If you want to have control over whether www.example.com/skates.asp?color=black&brand=riedell or www.example.com/skates.asp?brand=riedell&color=black gets shown in our search results, you may want to take action to mitigate your duplication. One way of letting us know which URL you prefer is by including the preferred URL in your Sitemap.

In step 3, if we aren't able to detect all the duplicates of a particular page, we won't be able to consolidate all of their properties. This may dilute the strength of that content's ranking signals by splitting them across multiple URLs."

Did you notice this line:

"You may want to take action to mitigate your duplication"

If a Joomla site is NOT using SEF's, then, we believe this problem is minimized as it's fairly easy to detect a website is using Joomla.  Google can see the "Url Parameters" and so, easily "cluster" duplicate urls into one.  Though, they still may not know which URL should be the parent.  That is where there site map tools can come in. At this time we like xMap for Joomla 1.5 site maps.  But there is still the problem as Google will likely find duplicate urls as they crawl your site.  Google, then has to "cluster", etc.  As they said, and we have seen, this will result in Page Rank dilution.

Now, on the other hand, if a Joomla site is using SEF's, Google will not see "URL Parameters", and so, will likely see multiple SEFS with the same content as "substantially the same" which is a penalty.

Given this, we strive for ZERO duplicate content via sh404 for Joomla 1.5 or our component serrbizSEF for Joomla 1.0 sites.

Both of these tools achieve nearly ZERO duplicate content as they do the work of associating duplicate urls into one SEF. In short, these tools give us better control of clustering. As webmasters, we like to have direct control of what Google and other search engines and humans see. It's better to have this control than to "hope" Google get's it right.

Additionally, understanding this problem is important.  Now that you know Joomla makes duplicate URLs, you can look for instances of duplication in your menu items.  If you identify any issues, you can take immeadite corrective steps such as copying and pasting SEFS and creating menu items as "external links" vs letting Joomla auto-generate the urls. In sh404 you can also set "aliases".  If that fails, you can also use .htaccess 301 redirects, etc.
 
In summary, our recommendation is to AVOID duplicate content whenever possible.  It will not only make your life easier when managing content and site maps, but also it will make Googles job easier.  Google will not have to "cluster" joomla's duplicate content urls, nor try to determine what is best.