An XML Sitemap is a simple document that lists all the pages in your website.

Believe it or not, Google is concerned about making sure webmasters have a way of communicating information that is important about their sites. Although Googlebot does a pretty decent job of finding and cataloging web pages on it's own, though it has very little ability to rate the relative importance of one page versus another. After all, many important pages on the Internet are not properly "optimized", and many of the people who couldn't care less about spending their time on linking campaigns create some of the best content.

Therefore, Google gives you the ability to tell them on a scale of 0.0 to 1.0 how important a given page is relative to all the others. Using this system, you might tell Google that your home page is a 1.0, each of your product sections is a 0.8, and each of your individual product pages is a 0.5. Pages like your company's address and contact information might only rate a 0.2.

A well executed sitemap designed in conjunction with a well implemented on-site link strategy, ensures that the right pages of your website are ranked the highest.