A sitemap provides an overview of website content in a manner similar to the contents page of a book.
Sections and pages are typically listed according to narrative flow, if the author intends for pages to be read in a specific order; or alphabetically or by chronology if content pages are essentially unrelated. The later is the case in news websites, where articles are often archived by topic, and then by title or publication date.
A sitemap is a useful way of orienting first-time users to the content of a website.
As webpage design must strike a balance between navigation and content, it is unlikely that top-level navigation options will enable a user to link directly from a landing page to the content they are seeking.
Providing a link to a sitemap enables a user to ‘get their bearings’—to more efficiently move around the website.
As the sole function of the sitemap is to explain how content has been structured, it also is an opportunity to expand navigation labels, that might otherwise be unclear.
For example, the label Articles may be as a top-level navigation link, and enable users familiar with the website to relocate the content they are seeking; for the first-time user, the sitemap may describe the intended audience and subject matter covered by the content in the Articles section.
Sitemaps are essential if a website uses frames.
<noframes> content (only shown if the web browser does not support frames) can link users to the sitemap
as an alternative means of linking to content pages.
Site maps are a secondary navigation feature: they don’t hurt people who don’t use them; they do help a few people.
an easy way for webmasters to inform search engines about pages on their sites that are available for crawling.