What is "canonical." And what do I need to do to fix it?

[KimCalvert]

I'm seeing about 450 warnings on this.

What is "Using rel=canonical suggests to search engines which URL should be seen as canonical."

And what do I need to do to fix it?

[ABCPS]

There is a very good explanation of "canonical" at http://tinyurl.com/38ycpw8\. by Jody Nimetz

The first part of it I have inserted here..... trust it helps:

Canonical URL: the search engine friendly URL that you want the search engines to treat as authoritative.  In other words, a canonical URL is the URL that you want visitors to see.

Quite often canonical URLs were used to describe the homepage.  The typical example used is that most people treat the following URLs as the same:

www.example.com
example.com
www.example.com/index.html
example.com/home.asp

The fact is that these are all different URLs.  From a search engine perspective, this can cause a bit of an issue.  Hence the idea of canonicalization.  Canonicalization is the process of picking the best URL (to present to the search engines) when there are multiple choices available.  Typically a search engine, such as Google will attempt to pick the best URL that they feel is the authority for that page.  However, sometimes they may in fact select the wrong one.  Now let’s suggest that you have product pages that depending on how the user navigated to the pager returns a different URL… same page but different URL, now we have a duplicate content issue.  Not to mention the nightmare for interlinking and external link inventories.

The easiest way to avoid this is to let the Search engines and the users know which is your “preferred URL” a.k.a canonical URL.............................

[mdreifenrath]

Anthony's response is correct for explaining what a canonical does. My response is for how to implement it. Say you have an online store that uses a bread crumb system. While you may have one main URL for a widget, multiple URLs could be created if visitors are taking multiple paths to find this widget. So say the main URL for this widget's page is: example.com/widget You could have many copies of this page on your website with different URLs. If you have URLs such as example.com/widget/1, example.com/widget/2, example.com/widget/3, and they all have the same content as example.com/widget, Google will see all of these pages as being duplicate content. So to take care of this you use a canonical. If you want example.com/widget to be the page that has the authority over the rest of the other URLs with the same content, you will need to create a canonical. The canonical for example.com/widget is: SEE EDIT BELOW Then you will want to take the canonical and put it somewhere inbetween the header for all of those URLs that have the same content. And as Anthony said www.example.com/widget is considered a different page than example.com/widget, so it would need the canonical from above as well, and the same goes for www. example.com/widget/1-3. http://www.ginzametrics.com/cheatsheet This link will take you to a great tool that generates meta tags and can also create a canonical link for you, if you don't want to type it all out. To make a canonical with the tool just copy and paste the main URL that you would like to use and it will create the canonical link below that you can copy and paste into the the pages head. EDIT: I don't think SEOmoz will let you post canonicals. But if you go the the link with the tool I provided you should still be able to create a canonical. It is a very simple and straight forward tool that can generate the canonical for you. Good luck.

[Dr-Pete]

Anthony's definitely got the basics covered. How to handle any particular situation can get pretty tricky. I wrote a post about it, and that post got very long very fast:

http://www.seomoz.org/blog/duplicate-content-in-a-post-panda-world

I took a quick look at your campaign (I have Staff access), and it seems your login page is carrying an event ID - so every event is creating a different URL, but they all land on one page. That could spin out 100s of duplicates on Google, and that login page has little or no search value. A canonical tag would definitely be a good bet here.

You may have other issues going on, but clean up one at a time - getting that number down can definitely be beneficial and help boost your ranking power.