A sitemap is a visual or text map of a site - an index of all pages organized in sections as they show up on the site. The sitemap is a single file and its presence may have a significant effect on the popularity of your site, especially if you have more content. It will make it possible for your visitors to look through the pages and find what they need way quicker, that will raise the possibility for them to return to the site or to share it with friends and colleagues. The sitemap is also required for search engines to index your site content better, which means that certain pages will appear in the results for specific searches, which might not happen without having a sitemap even if you have the required content. This is especially valid when you modify some pages because the sitemap informs the search engines that they need to crawl the site again so as to index the latest content. Having a sitemap these days is fundamental rather than an optional feature for every profitable Internet site.