To maximize your page ranking, the first and obvious point on to-do list is to implement the somehow mythical ‘finest page structure ever!’. However, in many cases it is not enough to avoid the occurrence of duplicate content: a situation when multiple links refer to the same page. It is a typical problem of eCommerce websites, as browsing the offer with different filters of products’ parameters produce new URLs that point the same or similar content.
For example, if you have an online shop (ecommerce) that sells skis for children, and one of your main sub pages is:
Using filters to specify the subtype of products displayed (e.g. of specific color, size, brand…) will not in fact change the content of a website appearing on the visitor’s screen (and in the search engine neither) – the title, description, text and structure remain all unaltered, but the URL address is different though:
In the example above the content appears duplicated across many pages, therefore in the worst case scenario, the website gets a penalty from Google for alleged use of cheating SEO techniques and attempts to manipulate the ranking. Nevertheless, it is not what happens often. The most common effect, less damaging but highly undesired anyway, is the lowered overall rank.
One may cope with it with a simple method of implementing canonical links tag to website’s code. Compare the simple domain address with a code containing canonical link tag:
Canonical parameter is a reference tag that Google promotes as the best solution to duplicate content. With such a tag, it is denoted that the address above is ‘the main one’ and that all similar addresses with, for example, automatically generated id should be ignored in search engine indexing.
Please note that using canonical links is not obligatory but helps with SEO. On the other hand, one may use other methods for similar purpose, such as 301 redirect, and some say that the latter should be used first.
There is no need to overdo with canonical links: one page may have only one canonical link; otherwise it may be ignored by search engine while crawling and indexing. It is good to think out which links should be tagged as canonical – the obvious answer is the most important sub pages and the home page, but it is not always the best solution.