It’s a complicated-sounding word that serves a very useful function in making sure both visitors and search engines see the URLs you intend
What is canonicalisation?
When you have the sameor very similar content accessible on multiple URLs, canonicalisation allows you to identify the page that you want both visitors and search engines to see.
These multiple pages are common on most sites, but can cause problems with organic visibility as the Page Authority of the content may be divided by search engines.
Without canonicalisation, a search engine can’t decide which version of the URL they should add in their index. If you have two or more pages resulting in the same content, its bots will assume one is a duplicate copy of the other.
To make sure the search engines are indexing the correct page, you need to select which variation of the URL you want to set as a canonical URL or canonicalised URL.
Canonicalisation ensures your site visitors always access the most relevant content, while keeping duplicated content out of the search engine index and consolidating a site’s authority and PageRank into one URL.
When Google ‘canonicalizes’ a url, we try to pick the url that seems like the best representative from that set
Matt Cutts, 2006
What’s the difference between a canonical tag and a 301 redirect?
The canonical tag is a metatag placed in the HTML header of a webpage. The tag, however, is not a redirect , so the users and search engines are not sent to another location, but a particular page is nominated for indexation with the search engines.
Although they’re both essentially navigation tools, canonical tags are distinct from 301 redirects, as 301s permanently redirect users and search engines to a particular page. A 301 redirect can be employed if the content of a page has been permanently moved or if you have created multiple versions of a home page and only want the users and search engines to see one version. This removes the possibility of the search engines interpreting several different URLs as having duplicate content.
The 301 redirect also allows you to more accurately monitor traffic to your homepage as everyone will be taken to one single URL address. Other reasons why you would use a 301 redirect is if you are moving your site from one domain to another, or if you want to direct users and search engines away from expired content on your site
Itching to find out more about canonicalisation and other aspects of on-page technical optimisation, download our SEO Uncovered: Techincal Optimisation eBook.
This is part of a series that that also includes chapters on:
- Analytics & Measurability
You can download the whole series here.