What is canonicalization?
Canonicalization is the process of nominating one single form of a webpage and having it load no matter what your visitors have actually typed in the URL.
Heres an example – Google sees all the different versions of your sites home page as different pages entirely so if a visitor types www.xyz.com, Google thinks thats different from just xyz.com; and it thinks that it is different from xyz.com/index; or www.xyz.com/index, or /index.php and so on.
Canonicalization is often needed for ecommerce sites. You’ve got this ONE nice bag that you want to appear on your website as http://www.shop.com/mybag.html
But that product has been categorised in your ecommerce platform as a handbag so it can also be found using your site as http://www.shop.com/handbag/mybag.html
Oh and its also classed as an oversized handbag so it appears also if you type in http://www.shop.com/handbag/oversized/mybag.html
How does canonicalization work?
The above page are basically the same. The only difference is the URL. In order for SEO to work properly they should be the exact same page – at least as far as search engines are concerned. You need to make sure that whateverversion of your URL your site visitors are typing in; they are still getting through to the same, canonical page. That is what Google calls it canonicalization of your content and pages.
Why should I bother about canonicalization?
Canonicalization of a URL is important for the SEO of your site. The canonical tag is applied to all the versions of your webpage that are not canonical. It tells Google that the page it has returned is one of the alternate versions, and that it should apply its metrics to a different page in lieu of the one it has found that is your nominated canonical home page.
Why is this important? Because when you have different versions of the same page loading under all those different URLs then Google can think you have duplicated a load of content which will affect your ranking. By making one address canonical, you are showing Google that there are copies of your home page out there that have been designed simply to give users access to the right content no matter what they type into the URL.