Canonicalisation – The Sacred Art of The rel=”canonical” Tag

What is Canonicalisation?

The concept of canonicalisation is not a complex one. Simply put, it refers to the process by which one variant of multiple URLs with the same content is given precedence within search engines over the others with the same content.

The most basic example would be when there are various examples of a homepage URL, for instance:

site.com
www.site.com
www.site.com/home
www.site.com/aspx.net
www.site.com/index.html

Rather than link value and PageRank value being recklessly scattered across each of these URLs, canonicalisation allows for the direction of all PageRank and link value to the one canonical page.

Though the outward perception of the existence of multiple URLs may seem harmless (users will reach the site despite the address they enter), search engines are not so indiscriminate.

How Can It Help?

As already pointed out, canonicalisation allows for the efficient focus of link and PageRank value to one canonical, or primary URL. In terms of link authority, having three links pointing to one canonical page is far preferential scenario in comparison with three links pointing to three variations of a page.

In addition to such benefits, the process can also prevent additional damage being done to your site where the demon of duplication is involved. Failure to define a canonical page can lead search engines to the conclusion that your site contains duplicate pages. And of course, duplication equals diminished rankings.

The existence of duplicated pages with no canonical tag directing search engine crawlers to the sovereign page will waste valuable crawler resources; because while the crawlers are rummaging around your site for duplicated pages, they could be crawling and indexing far more useful pages throughout your site.

For more info on canonicalisation best practice, Google Webmaster Tools provides an informative guide for all to see.

Alternative Uses

Of course, canonicalisation does not only apply to the existence of identical pages with differing URLs, there are other circumstances in which the implementation of a canonical tag is relevant. For example, sites with blog/news sections will use the rel=”canonical” tag (the tag used to denote the canonical page, submitted within the head section of the html) on each paginated list of blog or news content. This ensures that page 1 is the primary recipient of that all important PageRank and link juice.

So don't let link value and PageRank slip through your fingers needlessly, and ensure that you allow search engine crawlers to index the most important pages on your site by making use of this simple yet powerful tag.