Quick disclaimer: As Andre pointed out on my last post, everybody's situation is different. Many SEO recommendations can and should be customized to the site in question.
I have been having some back and forth with a former co-worker Matt about numerous basic-to-intermediate SEO concerns as he rolls out a new site. One of his recent concerns was about a) where to host mobile content and b) would that create duplicate content issues.
In order to identify valuable content, search engines often have to identify where content originates. Otherwise someone could come along and just copy someone else's great website and rank alongside them. This seems to present an obvious problem when delivering content to multiple mediums or platforms like mobile and desktops. Pages that are large, heavy with navigation, or just have a lot of resources associated with them make for a poor mobile experience. They were *designed* for the desktop.
In case you were not aware, if you do not provide a mobile-friendly version of your content (it may be too large, resource intensive, not WAP compliant, etc...), Google will automatically transcode your site to make it mobile friendly. You can actually view how your pages look transcoded with this tool.
But back to the question of duplicate content. The good news is that since Google is aware of this issue, you do not have to worry about the duplicate content issue. Google will not penalize for two pages with identical content as long as you consistently serve the same mobile-designed page to mobile users AND Google's mobile crawler.
I believe this immediately begs a follow up question: do you have to multiple versions of content for mobile (and other mediums) in today's web world? From a software perspective, keeping your content and presentation layers separate is step one toward solving this problem. If you are not in this place, this is step one and you can probably let Google transcode for you while you address this.
If your content is separate, the next question is a content location question. In the recent past the trend seems to be to serve the mobile content from a different URL (for example at a subdomain like http://m.example.com/ for mobile and http://www.example.com/ for desktop). In this case, you can redirect mobile users by identifying the user agent. It is considered best practice in this scenario to provide a link back to the regular site from here, allowing the user to pick the presentation.
Another way to handle this is to use the canonical and alternate link elements. Here they discuss using it for languages, but you can see how this translates to any medium. Benj Arriola's great article discusses various technical solutions to the mobile duplicate content problem.
But to me the best answer is to serve the same content at the same location and merely adjust presentation. Google's John Mueller endorsed this notion in a Google Q&A Buzz in June:
Even better however is to use the same URLs and to show the appropriate version of the content without a redirect :).
You can use CSS or other rendering techniques to serve up the exact same content at the same location, and only switching your presentation based on the medium. This will also force you to get your content and presentation layers separate, which you really ought to do.
Some other good resources on this topic:
- Are your mobile pages ranking, and if so, how well? Test them on a desktop with Google's mobile search emulator.
- A great webmaster central blog post on making websites mobile friendly
- This is slightly old news, but if you are using sitemaps to tell Google where your mobile pages are, you can consolidate your sitemaps.