10 Must Know Image Optimization Tips - Image SEO. Getting On-Page SEO Right in 2012 and Beyond - Whiteboard Friday. Configuring URL Parameters in Webmaster Tools. URL parameters - Webmaster Tools Help. Google’s goal is to crawl your site as efficiently as possible.
Crawling and indexing pages with identical content is an inefficient use of our resources. It can limit the number of pages we can crawl on your site, and duplicate content in our index can hinder your pages' performance in our search results. Duplicate content often occurs when sites make the same content available via different URLs—for example, by using session IDs or other parameters, like this: In this case, all these URLs point to the same content: a collection of real green dresses. When Google detects duplicate content, such as variations caused by URL parameters, we group the duplicate URLs into one cluster and select what we think is the "best" URL to represent the cluster in search results.