A site map is a representation of a site's structure used for navigation. This provides a top-down overview of the site's content at a glance. Using a site map, visitors can jump directly to any page listed.
A site map is often afforded its own page, but it may also appear, in part, on other pages. Site maps should therefore be fairly simple and easy to scan. It's also critical that labels used in the site map match the main navigation categories, as well as page titles.
One line of reasoning is that if your main site navigation matches user needs, a site map is not necessary. Ideally, this may be true, but it isn't always the case. Sites with a great deal of content and a wide variety of user types may not be able to predict every information need for every visitor in every situation. A site map could help.
Site maps have gone in and out of style. In the early years of e-commerce, many sites included one. But creating and maintaining a site map is not easy and sometimes costly. The investment often doesn't match the benefit.
More recently, site maps have been recognized as a means of optimizing search engine indexing. Search engines can get a better overview of your site's total content via a site map. So, although site visitors may not use them often, site maps may have other benefits. You'll need to weigh the advantages and disadvantages carefully.
A fundamental question in creating a site map is that of granularity. It may not be possible, nor desirable, to list every ...