A hierarchical list of web pages that belong to a site. HTML versions are typically part of a site’s navigation.
A Sitemap allows creating a file hosted among other files in your account that informs the search engines of all pages your website contains. In other words, we may say that it provides the search engine with detailed information about the content of your website.
Sitemaps are mainly used to improve the index process of a website by search engines. They are also used to provide accessibility to certain pages. For example, pages that are not accessible via the website’s menus can be indexed by the search engines if you want.
The Sitemap does not affect the normal way crawler bots index of a page but it just extends the visibility and accessibility of the website content.
Sitemap Protocol requires definite tags to be present in website’s XML file in order to be properly recognized. The file should be also UTF-8 encoded.
XML schema is used Search engines to define the elements and attributes that can appear in a Sitemap file.
Google schema can be downloaded from the links:
For Sitemaps: Sitemap schema from SiteMap.org
For Sitemap index files: Sitemap Index schema from SiteMap.org
There are many tools available to help in validating the structure of a Sitemap based on this schema. A list of XML-related tools can be found.
HTML Sitemap Generator tool can be used to make HTML sitemap web pages for a website. A single webpage which lists all the web pages in a simple manner eases the job of the search engines when crawling the site.