A sitemap is an XML file that lists URLs for a site, along with additional information about each URL. Sitemaps give Google and other search engines important information about your website, including:

• A complete list of all URLs on your site, including URLs that may not be discoverable by Google's normal crawling process (for example, non-text pages or URLs containing several parameters.)
• How often the pages on your site change. For example, you might update your product page daily, but update your About Me page only once every few months.
• The date each page was last modified.
• The relative importance of pages on your site. For example, your home page might have a relative importance of 1.0, category pages have an importance of 0.8, and individual blog entries or product pages have an importance of 0.5. This priority ranking only indicates the importance of a particular URL relative to other URLs on your site, and doesn't impact the ranking of your pages in search results

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.
• Your site has a large archive of content pages that are not well linked to each other, or are not linked at all.

While sitemaps can make for speedier crawling and indexing of your pages, there are many other factors that influence the crawling/indexing processes. These other factors include:

• How many sites link to you
• Whether your content is unique and relevant
• Our ability to crawl the pages successfully
• Everything outlined in our webmaster guidelines.

A sitemap provides an additional view into your site (just as your home page and HTML site map do), but sitemaps do not replace our normal methods of crawling the web. Google still searches and indexes your sites in the normal way, whether or not you use this program, and sites are never penalized for using this service. We can't make any predictions or guarantees about when or if your URLs will be crawled or added to our index but over time, as we refine our processes and better understand webmasters' needs, we expect both coverage and time-to-index to improve.

Google adheres to Sitemap Protocol 0.9 as defined by sitemaps.org. Sitemaps created for Google using Sitemap Protocol 0.9 are therefore compatible with other search engines that adopt the standards of sitemaps.org.