Domain canonicalisation is the nomination of a particular domain as the authority for website content.
Shown below are possible variations of the same domain. Each could be showing the same content if the appropriate redirects have not been put in place.
- http://example.com
- http://www.example.com
- http://www.example.com/
- http://www.example.com/?source=asdf
Internet search engines mark down web sites which have duplication of content.
Where a web site serves the same content for the domain with and without the www it can be taken as duplication of content.
Having the same content under different domains can also make it hard for a search engine to decide to which domain, or page, the search results should link to.
If the content is to be the same for both forms of the domain (with and without www) then one should be directed as a permanent redirect into the other.
Some prefer the full domain including the www prefix, whilst others advocate the reduced version. I’ve not seen commentary regards the search engines biased to either. It maybe better to use public expectation when deciding which to use.
By indicating which domain variation is the canonical variant it ensures that full SEO recognition is given to that domain. Thus avoiding splitting the SEO assigned value across multiple equivalent pages.
This allows for the same, or very similar, content to be available on different domains. For example where both example.com and www.example.com are available to view full recognition can be given to the preferred one.
Canonical indication can also be used to counter the duplication of content either consciously or by content copying to other domains.
By the use of domain canonicalisation its possible to ensure that search engines direct the visitor to just the one domain, giving priority.
Shown below is an example of the inclusion of canonicalisation, its added inside the <head> section of the website’s HTML code.
<link rel="canonical" href="https://www.vntweb.co.uk/?p=3835" />
Highlighting the importance of domain canonicalisation Google has a webmaster blog Specify your canonical.
