From Seo Wiki - Search Engine Optimization and Programming Languages
A site map (or sitemap) is a list of pages of a web site accessible to crawlers or users. It can be either a document in any form used as a planning tool for web design, or a web page that lists the pages on a web site, typically organized in hierarchical fashion. This helps visitors and search engine bots find pages on the site.
While some developers argue that site index is a more appropriately used term to relay page function, web visitors are used to seeing each term and generally associate both as one and the same. However, a site index is often used to mean an A-Z index that provides access to particular content, while a site map provides a general top-down view of the overall site contents.
Benefits of sitemaps
They also act as a navigation aid  by providing an overview of a site's content at a single glance.
Most search engines will only follow a finite number of links from a page, so if the number of links is very large, the site map may be required so that search engines and visitors can access all content on the site.
Google introduced Google Sitemaps so web developers can publish lists of links from across their sites. The basic premise is that some sites have a large number of dynamic pages that are only available through the use of forms and user entries. The Sitemap files can then be used to indicate to a web crawler how such pages can be found. Google, Bing, Yahoo and Ask now jointly support the Sitemaps protocol.
Since Bing, Yahoo, Ask, and Google use the same protocol, having a Sitemap lets the four biggest search engines have the updated page information. Sitemaps do not guarantee all links will be crawled, and being crawled does not guarantee indexing. However, a Sitemap is still the best insurance for getting a search engine to learn about your entire site.
XML Sitemaps have replaced the older method of "submitting to search engines" by filling out a form on the search engine's submission page. Now web developers submit a Sitemap directly, or wait for search engines to find it.
XML (extensible markup language) is much more precise than HTML coding. Errors are not tolerated, and so syntax must be exact. It is advised to use an XML syntax validator such as the free one found at: http://validator.w3.org
Benefits of Sitemaps to Search Optimize Flash sites
Below is an example of a validated XML sitemap for a simple three page web site. Sitemaps are a useful tool for making sites built in Flash and other non-html languages search-able. Note that because the website's navigation is built with Flash (Adobe), the initial homepage of a site developed in this way would probably be found by an automated search program (ref: bot) However, the subsequent pages are unlikely to be found without an XML sitemap. You can see the original site's animated navigation here: http://www.magnity.com
XML SiteMap example:
<?xml version="1.0" encoding="UTF-8"?>
There are automated XML site map generators available (both as software and web applications) for more complex sites.
More information defining the field operations and other Sitemap options are defined at http://www.sitemaps.org (Sitemaps.org: Google, Inc., Yahoo, Inc., and Microsoft Corporation)
See also [Robots.txt files], which can be used to identify sitemaps on the server.
- Search engine optimization
- Sitemaps, a standard for URL inclusion
- Biositemap, a protocol for broadcasting and disseminating information about computational biology resources (data, software tools and web-services).
- PowerMapper, a tool for automatically creating site maps with thumbnails for each page
- Common Official Website - Jointly maintained website by Google, Yahoo, MSN for an XML sitemap format.
- / Sitemap generators at the Open Directory Project
- Tools and tutorial Helping to build a cross-systems sitemap generator.cs:Sitemap