The Google Webmaster Central Blog has made a Sitemaps FAQs blog post. In this blog post, where Google responds to some of the most asked questions on the Sitemaps protocol and how Google supports it.
Here’r some the questions:
Q: I submitted a Sitemap, but my URLs haven't been [crawled/indexed] yet. Isn't that what a Sitemap is for?
A: Submitting a Sitemap helps you make sure Google knows about the URLs on your site. It can be especially helpful if your content is not easily discoverable by our crawler (such as pages accessible only through a form). It is not, however, a guarantee that those URLs will be crawled or indexed. We use information from Sitemaps to augment our usual crawl and discovery processes. Learn more.
Q: If it doesn't get me automatically crawled and indexed, what does a Sitemap do?
A: Sitemaps give information to Google to help us better understand your site. This can include making sure we know about all your URLs, how often and when they're updated, and what their relative importance is. Also, if you submit your Sitemap via Webmaster Tools, we'll show you stats such as how many of your Sitemap's URLs are indexed. Learn more.
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