What is Canoncalisation?
Canonicalisation is the process of choosing one URL as the preferred URL when there are several choices.
Awkwardly in the SEO industry we talk about canonicalisation as the name of the issue, but in actual fact canonicalisation is the solution.
Most websites will have canonicalisation issues, in particular on the homepage.
For example the homepage can be found on:
http://vervesearch.com (note! Without the www)
and often also variations such as:
or /home.asp /home.php etc etc
The problem with this is that when the search engine spiders (also often referred to as bots) come to your website, they will see all of these URLs with the same content. As the search engines have billions of web pages indexed, they are understandably not keen on having duplication of the same content.
So the cute Google spider (spider image source: Moz.com) will CHOOSE ONE URL to index, and as you haven’t told him which one you prefer him to index it could be either of these URLs (although most often it’s the URL with the most links, but not always).
What is the problem with this?
The biggest issue with this is LOSS of Link Equity. In the below example the search engine spider chose the http://vervesearch.com URL to index, now this page only had 45 links while most people that linked to the site linked to the http://www.vervesearch.com URL.