I found this information while doing some research. Google has an amazing amount of very informative information this is just one of many articles.
I though it was a really good entry to my blog. This is for those of you who have a website that has a lot of diversified pages. Not all website need a sitemap it just depends on what pages you really want indexed. Some SEO experts (I have read differing opinions as I have researched) believe that you only want your main pages index - and that will give you a higher rating.
Other feel it doesn't seem to matter.
Quoted from http://www.google.com/support/webmasters/bin/answer.py?answer=40318&hl=en:
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.
You can also use a Sitemap to provide Google with additional information about your pages, including:
- 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 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 provide additional information about your site to Google, complementing our normal methods of crawling the web. We expect they will help us crawl more of your site and in a more timely fashion, but we can't guarantee that URLs from your Sitemap will be added to the Google index. Sites are never penalized for submitting Sitemaps.
Google adheres to Sitemap Protocol 0.9 as defined by sitemaps.org. The Sitemap Protocol is a dialect of XML for summarizing Sitemap information that is relevant to web crawlers. Sitemaps created for Google using Sitemap Protocol 0.9 are therefore compatible with other search engines that adopt the standards of sitemaps.org.
While a standard Sitemap works for most sites, you can also create and submit specialized Sitemaps for certain types of content. These Sitemap formats are specific to Google and are not used by other search engines. They're a good way to give Google detailed information about specific content types. For example, publishers can use News Sitemaps to give Google information that can appear in Google News search results, such as publication date, keywords, and stock ticker symbol. Sitemap formats include: