What is an XML Sitemap
An XML Sitemap allows you to give search engine crawlers more information about the URL’s that they are crawling on your website. Information can include when the URL was last updated, how often it is modified and how important it is in relation to the other URL’s of the website. It also allows website URL’s which were previously not included in the browser interface and files such as flash and Ajax, to be crawled.
The XML sitemap is an inclusion protocol tool and as such compliments the robots.txt exclusion protocol tool. Including a sitemap on your website does guarantee that all of the pages will be indexed in Google; it just increases the chance of this happening by letting the spiders crawl your website freely and be pointed in the right direction. As sitemaps list all of the URL’s of a website, even those pages which are not able to be found via the browsable interface can be crawled.