Site map are basically two types HTML site map and XML site map. HTML site map is acronym Hyper Text Markup Language site map and XML site map is acronym Extensible Markup Language site map.
Site map are use to list the entire web site page in single page. There all the links is listed in hierarchy and also add description of all the pages. The HTML site map is added by user point of view to find the entire page in single page to easily navigate. That way HTML site map is created by user indexing crawler and ranking point of view. XML site map is created in a site not for user but only search engine crawler points of view, URL of the web site are very easily indexed. XML site is submitted in Google Yahoo! and MSN search engine this will not only help to de indexing of your site but also ranking and also visibility in search engine.