A Sitemap is a file where you provide information about pages, videos, and other files on your site, and the relationships between them. Search engines like Google have read this file to crawl your site. The Sitemap tells Google which pages and files you think are important for your site, and provides important information about these files: for example, pages, where the page was last updated, how often the page was changed, and any other forms of page language.
You can use the Sitemap to provide information about specific types of content on your pages, including video and image content. For example:
Site video insertion can determine video performance time, category, and age-appropriate rating.
Image mapping of the site may include the subject matter of the image, type, and license.
Do I need a sitemap?
If your site's pages are properly linked, Google can usually discover most of your site. Even so, a sitemap can improve the crawling of larger or more complex sites, or more specialized files.