For SEO purposes, canonical issues refer to inaccuracies in web traffic reporting and other SEO problems related to the URL the user enters into a browser to reach a site. Browsers treat www.yoursite.com and yoursite.com as if they are the same, but for analytical programs, these are two different domains. Without proper fixes in place, if half of your users use one form of the address and the other half use the other form, then your site would appear to be half a popular than it really is.
