WAI Definition (Checkpoint 13.3)
Provide information about the general layout of a site (e.g., a site map or table of contents).
Provide an overview of the site's structure which summarizes the contents of the site.
An overview of the site's structure and content makes navigation easier. For example, providing a site map or table of contents allows the user to browse through key sections of the site without having to navigate through each individual page. This is also very helpful for people using assistive technologies, such as a screen reader. For example, the screen reader can scan the site map, giving the user an overall idea of the contents so that he/she can rapidly determine the location of the information wanted and go directly to that page.
A table of contents or site map can assist people who have become confused, disoriented or have gotten lost during the navigation process.
There should be a sitemap on any site with pages that cannot be accessed from the navigation bar's default state or the homepage.
Check the site.
A site map or table of contents exists if the site has pages that cannot be accessed from the navigation bar's default state or the homepage.