By standard definition, 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.
According to Google,
“Sitemaps are a way to tell Google about pages on your site we might not otherwise discover. In its simplest terms, a XML Sitemap‚ usually called Sitemap, with a capital S, 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.
In addition, you can also use Sitemaps to provide Google with metadata about specific types of content on your site, including video, images, mobile, News, software source code, and geographical (KML). For example, a video Sitemap entry can specify the running time, category, and family-friendly status of a video; an image Sitemap entry can provide information about an image’s subject matter, type, and license. You can also use a Sitemap to provide additional information about your site, such as the date it was last updated, and how often you expect the page to change. We recommend that you use a separate Sitemap to submit News information.
Sitemaps are particularly helpful if:
Google doesn’t guarantee that we’ll crawl or index all of your URLs. However, we use the data in your Sitemap to learn about your site’s structure, which will allow us to improve our crawler schedule and do a better job crawling your site in the future. In most cases, webmasters will benefit from Sitemap submission, and in no case will you be penalized for it.
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.
The most important part of the above Google Sitemap definition is “Google doesn’t guarantee that we’ll crawl or index all of your URLs. However, we use the data in your Sitemap to learn about your site’s structure, which will allow us to improve our crawler schedule and do a better job crawling your site in the future. In most cases, webmasters will benefit from Sitemap submission, and in no case will you be penalized for it.”
Since the sitemaps main purpose is make it easier for search engine crawlers (spiders) to index your site, most sites would benefit from having a Sitemap that is formatted in a way that search engines prefer. Yes, you can have a HTML sitemap for your human visitors but unless you are directing web traffic there specificall through your menue structure or other means, most humans visitors basically click through your site via the menu path your want them to use. An XML sitemap, one written specificall for search engines such as Google, Yahoo, Bing etc, is an XML file that lists URLs for a site, along with additional information about each URL. XML sitemaps give Google and other search engines important information about your website, including things such as: