When mobile search engine optimization even first became a thing, a lot of us SEO nerds worried incessantly about the duplicate content issue. When two different URLs provide the exact same content, they end up splitting the total value of the content in SEO terms, making it harder for either page to achieve strong performance on the search engine results pages. Make no mistake, this is certainly how things work in ordinary SEO.

The truth is, search engines are starting to wise up about the difference between traditional browsing and mobile browsing. In December Google overhauled the way it processes redirection, (in the “Old Possum” update) making it far easier for a mobile site to achieve strong search rankings using the same content featured on a traditional desktop-oriented site.

The crucial factor in achieving this kind of performance is using canonical tags properly. These ensure that Google and other search engines treat mobile and desktop pages as entirely separate entities, even when there are content overlap issues. This is entirely reasonable, given the huge gulf that lies between the worlds of desktop and mobile searching.

This doesn’t mean that duplicate content ceases to be a problem in mobile optimization, though! There are some unique issues caused by mobile formatting that never come up in traditional SEO work. In most cases, failure to address these problems degrades mobile ranking by splitting up link equity between different pages on the same mobile site.

While proper redirection will take a lot of the sting out of these problems, it can still be tough to push a unique mobile page to high rankings without addressing them. It can even be hard to use mobile URLs to feed link equity into your primary site if you don’t watch out for these issues.

Interstitial Pages Promoting Apps

If you visit Open Table on a smartphone, you’re directed to a page promoting the site’s custom app. The site is smart enough to detect what operating system your device uses, so Android and iPhone users each get a unique version of the promotional page. The problem is that both interstitial pages are indexed by search engines.

If you were in the SEO game several years ago, you might remember similar trouble coming from intro pages that used Flash. It’s impossible to prevent users from sharing a link to a platform-specific page rather than your main page. This means you get badly-fragmented link equity and seriously degraded performance on one of the most important URLs on your site.

One strategy for avoiding this issue is abandoning the idea of an interstitial page and integrating all app promotion into the main page. Divorcing the mobile web experience from the app is another possibility. When this is impossible, it’s generally smart to avoid splitting up information onto separate pages to address users with different platforms.

Legacy Transcoder Duplication

Companies took some questionable steps in the rush to provide mobile content to early adopters of Internet-enabled mobile browsing, and the repercussions continue to this day. This led a lot of companies to rely on transcoders (e.g. Usablenet) to create mobile sites. Time has moved on, and today virtually everyone develops their own mobile content.

The problem is that a lot of those early transcoded pages are still being indexed by Google. When it features the same content as later, custom-built mobile content, it splits up link equity. Because the the transcoded material is so old, it even scores as more trustworthy in the eyes of Google.

Sears makes an excellent example here. Using jQuery, they’ve created an extensive mobile site featuring more than 300,000 indexed pages. The problem is that their old Usablenet site is still stuck in the Google index, with 180,000 pages crammed full of potentially-troublesome content.

Carrier Pages

Another leftover from the very earliest days of mobile browsing is the carrier-specific page. A lot of companies created customized pages to use with different carriers, e.g. a page designed exclusively for use with T-Mobile’s “T-Zone.” Even though Google and other search engines have been warning about the possible negative impact this practice can have, some companies still generate duplicate content and spread it around on carrier-specific pages.

The best way to avoid this is to stop creating carrier pages. This isn’t always an option, though. The canonical tag should be used aggressively to minimize the potential damage from duplicate content. Parameter-based pages can also take advantage of parameter handling procedures to note duplicate content and see that it’s parsed properly by the search engines.

Additional Confusion Between Domains

The problems presented by mobile content that was transcoded in the past were outlined above. That’s not the only way that cross-domain duplication can become an issue, though. In order to spread a wide net and capture every possible visitor, a lot of sites end up posting the same content to several different domains.

Take CBS Sports as an example. Their mobile site is directly accessible from m.cbssports.com. If you’re using a T-Mobile phone, though, you have a convenient link on your deck to reach the same content. Hitting that link takes you cbstmobile.mo2do.net/?src=tmobile, though. Finally, what if you run a search for “cbs sports mobile?” You reach the same content again, but this time the URL you get is wap.sportsline.com.

You can see the issue here; search engine confusion and a serious breakdown in rankings on competitive search terms is all too likely. Once again, the answer is to be rigorous and consistent in deploying canonical tags and / or parameter handling.

MARCH 2015 UPDATE: Mobile websites are so five years ago. Just go have a proper mobile responsive website built and to make sure that it is mobile friendly and in favor of what Google is looking for, get it tested.

The Dangers of Pride: Showcasing the Mobile Site on the Desktop Site

There are limits to the relevance-detecting powers of the Google algorithm. When a user searches for a mobile version of a popular site, it’s entirely possible that the top result will actually be a desktop page created to promote the mobile site instead of the mobile site itself. The NFL, the NBA, and MLB all have promotional pages for their mobile versions that can cause this kind of confusion.

The effects of this problem are largely one-way. The scoring of the desktop pages is in no danger; it’s the mobile site that suffers. These false positives rob the mobile sites of link equity and reduce their overall rankings.

This is one case where Google hasn’t been clear about the best practices for tagging out these “showcase” pages. How the canonical tag is going to be treated in these situations is unclear; hopefully the showcase pages can either be excluded entirely or their presence can redirect mobile users to the proper mobile site.

The Fight Between Apps and Pages: Round Two

Some companies have decided to abandon web content entirely and focus all of their attention on their apps. There are plenty of shortcomings to this strategy. Considered strictly in terms of optimization, the biggest one is that app-exclusive content exists in a bubble where it can’t be connected to any other content.

Although this avoids the problem of content duplication, it also makes it impossible to improve rankings on competitive search terms. The bottom line is that it takes this valuable content out of the SEO game entirely.

While apps are certainly the appropriate venue for functions that can’t be provided through mobile web content, it’s just not sensible to use them in order to share the same content from your main site with mobile users. It’s far better to invest the effort in creating a mobile-friendly version of the site and then protecting it from duplicate content issues by creating mobile centric copy, graphics, and videos.

WAP Sites and Duplication

Before the rise of smartphones, feature phones offered mobile users a way to access online content no matter where they were. This led to to the creation of the WAP protocol for specialized mobile-only information sharing. Although it worked effectively enough, it was soon made obsolete by the rise of the smartphone. Proper mobile design allows the same URLs to serve content to both smartphone and feature phone users, making the use of wap.com subdomains completely unnecessary.

There are still nearly eight million wap.*.com pages floating around the Google index, though. If your company owns any of them, make sure that you conserve your link equity by adding canonical tags that point to your primary mobile site in the appropriate locations.