Marketers at international companies want Google's search engine to know when one Web site is related to another, or when someone searching in the U.S. should see the Web site that is intended for the
U.S. rather than another country. For example, using structured data tags tell Google how to direct the searcher to the correct local version of the site. Matt Cutts explains how Google views the
relationship between sites and what tags to use in a Webmaster video on YouTube.
Read the whole story at Google Webmaster Help »