What’s a Canonical Page Exactly?

It’s a pretty simple concept actually. When you have web pages with similar content, a canonical page is the one that is situated to rank best, making it the preferred page.

Why is a Canonical Page Necessary?

While original content is the goal of any successful website, in certain circumstances it is not realistic. Oftentimes, sites cannot avoid having a handful of pages with similar content. Without a canonical page or tag, the site could potentially be penalized for duplicate content.
If search engines like Google are aware of these pages having similar content, the best option would be to only index one of the pages for search results. Most search engines will make the choice for you through their algorithms. However, if you prefer to chose to specify which page is a canonical to the search engines, provide a (to the preferred page) along with the rel=”canonical” attribute directly to the area of the non-canonical version of the page. By adding this attribute and link to the HTML of the page, it allows site owners to identify specific sets of similar or identical content, as well as the ability to suggest to Google: “While many of these pages have identical or similar content, this is the page that is most useful. This page should be prioritized as the ideal page for search results.”

How to Specify a Canonical Web Page

There are two ways to specify a canonical URL:

The first is to access the non-canonical version of the HTML pages and add the rel=”canonical” link directly to the section. Then add a canonical link to the HTML of the page (example: http://www.examplesite.net/item.php?item=bacon), by creating a element: Once done, then copy this link code directly into the area for all non-canonical variants of the page, such as http://www.examplesite.net/item.php?item=bacon&sort=price. If you have published content on both http://www.examplesite.net/item.php?item=bacon and https://www.examplesite.net/item.php?item=bacon, you are able to specify which is the canonical version of the page. Do this by creating the element once again: Then put this in the section of https://www.examplesite.net/item.php?item=bacon. Indicate URL in it’s canonical version by adding rel=”canonical” to the HTTP header. By inputting rel=”canonical” into the head area of a page is make it helpful for the HTML content, However, this cannot be utilized in PDF formats or other types of files that are indexed via Google Web Search. When faced with these types of cases, indicate that it is a canonical URL by putting a Link rel=”canonical” into the HTTP header. This can be done like this (please note: to use this specific option, you will have to configure your server first): Link: <http://www.examplesite.net/downloads/bacon-pdf-white-papers.pdf>; rel=”canonical”

As it currently stands, Google only supports these types elements for link headers through web search results.

So is Google Suggesting or Demanding We Do This?

First and foremost, this is an option. However, when Google comes out and say “Hey! Check out this cool ‘suggestion’ guys! You might want to think about using it.” It means, you should use it when possible. Basically this takes the guessing out of which page you want indexed as the most relevant page for the subject matter. If you chose to go without adding these for pages with similar content, then Google will make the call for you.
Remember, when indexing, ranking, and determining what URL sets have identical content, Google takes into account a variety of signals. By adding these tags, you can make one of the big decisions yourself, instead of the search engine, saving you headaches down the road.

Can the Canonical Link be Absolute or Relative?

The canonical tag can be utilized for both absolute or relative links. However, Google recommends that users use absolute links, this will minimize the potential difficulties or confusion. If your document requires a base link for this situation, all relative links will also be relative to the base link.

Does the Content on the Other Web Pages have to be the Similar to the Content on the Page with the Canonical Tag?

Yes it does. The canonical attribute should only be used when specifying which is the preferred page of a set that has identical content. Keep in mind, the word identical is more of a blanket term in the sense, since minor differences, and sort order, do not disqualify pages.
For example, if a website has a select number of pages that have the same type of shirt, with the only difference being the color of the shirt, it would make sense to designate the most popular shirt color as the canonical version. This way Google will be much more likely to display that page more prominently in search results. However, the canonical tag wouldn’t be an option if this same website wanted a polo shirt page to have a higher rank than the t-shirt page.

What if a Canonical Link Directs to a Page that is Non-existent? What if more than a Single Page within a Set is Designated as a Canonical Page?

Google tries it’s hardest to algorithmically figure out the correct canonical page, just like they’ve done before the tag. So all hope is not lost in this circumstance.

Is it Possible for Google to Follow a Series of Canonical Link Designations?

To a certain extent yes, however, to make certain everything is up to optimal canonicalization, Google strongly recommends users update their links to direct to one specified canonical page.
Is it possible for a canonical link to be used to help point to a canonical URL that is on a different domain?

In certain circumstances where it is not easy to establish redirects, canonical URLs could help.
It could be that you need to move to a different domain name and are using a server that can’t establish redirects on the server-side. In this type of circumstance, you may use the canonical link to identify the correct URL of the preferred domain you want to index. Keep in mind however, the canonical link is identified as a helpful hint or tip to the search engine, and not as a guaranteed redirect, although Google tries to follow it as much as possible.

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