http://www.google.com/support/webmasters/b...amp;topic=13450


What is a Sitemap file and why should I have one?

In general, there are two types of sitemaps. The first type of sitemap is a HTML page listing the pages of your site - often by section - and is meant to help users find the information they need.

XML Sitemaps - usually called Sitemaps, with a capital S - are a way for you to give Google information about your site. This is the type of Sitemap we'll be discussing in this article.

In its simplest terms, a Sitemap is a list of the pages on your website. Creating and submitting a Sitemap helps make sure that Google knows about all the pages on your site, including URLs that may not be discoverable by Google's normal crawling process.

Sitemaps are particularly helpful if:

* Your site has dynamic content.
* Your site has pages that aren't easily discovered by Googlebot during the crawl process - for example, pages featuring rich AJAX or Flash.
* Your site is new and has few links to it. (Googlebot crawls the web by following links from one page to another, so if your site isn't well linked, it may be hard for us to discover it.)
* Your site has a large archive of content pages that are not well linked to each other, or are not linked at all.