Definition of the canonical URL (canonical URL)
Americans spent in forums referencing, we hear about canonical URL. My dictionary says that means according to canonical rules, with the standard.
We say that a URL is a canonical URL address when it is “official” web page, that it is best to use to access the corresponding content.
Duplicates (duplicate content)
Detect duplicates, that is to say, the web pages contained identical or nearly identical tasks is part of a search engine. Indeed, when a user does a search, it does not want to get several times the same result. The search engines must only display a single content in the results.
Various techniques exist to measure the similarity of web pages. In the context of the canonical URL, we are interested only in case the similarity is complete: if exactly the same content is detected at several different addresses, a search engine like Google will display once mentioning only the address he considers to be the canonical URL.
And canonical URL redirection
If you redirect an address A to address B, the page displayed in a browser will be the same as the user types the address A and address B. The canonical URL problem then arises as in the case of redirects.
If both addresses are in the same area, for Google, the canonical URL address will be doing the redirect if it’s a 302 redirect and the destination address of the redirect if it’s a 301 that was used unless it is much longer than doing the redirect address.
If both addresses belong to different domains, Google will always choose the destination address of the redirect, unless it is much longer than doing the redirect address.
Google – as users – thus favors the short addresses and destination addresses redirects.
Canonical URL and link weights.
If the addresses A and B correspond to the same content and if the canonical URL is the address A, Google will assign to the canonical URL all the weight of links to A and B. In short, all the weight of inbound links goes to the canonical URL.
Undetected duplicate content by Google
Google does not detect immediately any case of duplicate content. If Google does not realize that many of your pages have the same content, it does not benefit you, however.
Suppose your pages A and B display the same content and so many inbound links that go to A and to B. The rankings in Google on page A benefit only links to that of A and B receive only page links to B, whereas if Google detected duplicate content or if you were doing a redirect, Google would allocate all Incoming links of A and B to the canonical URL.
Rules of sound management URLs
The goal is that you loose control of the situation and take Google as the canonical URL for you.
Rule 1. Above all, try to avoid that two addresses displayed the same content. But realistically, it is not always possible to avoid “duplicate content” and any redirects.
Rule 2. Choose a redirect rather than having two addresses not redirected that display the same content.
Rule 3. You should choose the 301 redirect and make sure that the destination address is not substantially longer than doing the redirect address. The canonical URL is the destination address of the redirect.
Rule 4. Ensure that maximum links point directly to the canonical URL. Wherever possible, replace the existing links pointing to another address by links to the canonical URL.