Google (along with Microsoft and Yahoo, it seems) have just announced they now support a format that allows you to publicly specify your preferred version of a URL. If you have multiple pages that have similar content you can now let Google know which is the one you wish them to index.
The idea is a new <link> tag that specifies the preferred version of a page inside the <head> tags, as follows:
<link rel=”canonical” href=”http://www.thinksynergy.co.uk/2009/02/11/twitter/”/>
At first glance I was wondering what all the fuss is about, as to be honest most of us have done a reasonable job of cutting out the duplicate content in our blogs anyway. Once thing I overlooked was the use of Google analytics campaigns (along with any other campaigns). This could lead to your URL being tagged (and indexed) as:
There are two issues with this. The first is that the above indexed URL could be (to what extent, only Google can answer) penalised as duplicate content. Secondly, if it is not being penalised, it is certainly attracting the PageRank that should be aimed at the “official” page.
By using the canonical tag the tagged URL will now tell Google the preferred version of itself, thus putting the PageRank where it should be and avoiding any possibility of being kicked in the backside for duplicate content.
This is a subject that has been discussed a few times on Nice2all, as WordPress seems a hot bed of duplicate content and it is a challenge to cut out as much of it as possible. I imagine with this new method it will be possible to put this issue to bed once and for all, although I haven’t had time to test it out just yet.
I am a bit cynical of the effect of duplicate content, I actually think Google deals with it quite well and people are not punished as much as they may think, but this is a very easy tag to implement and whatever we can do to make the search engines job easier the better in terms of reward, I guess.