Deciding what to include in a sitemap file
When you create a sitemap file, you need to take care in situations where your site has multiple URLs that refer to one piece of content: include only the preferred (canonical) version of the URL, as the search engines may assume that the URL specified in a sitemap file is the preferred form of the URL for the content. You can use the sitemap file to indicate to the search engines which URL points to the preferred version of a given page.
Also, be careful about what not to include. For example, do not include multiple URLs that point to identical content, and leave out pages that are simply pagination pages (or alternate sort orders for the same content) and any low-value pages on your site. Last but not least, make sure that none of the URLs listed in the sitemap file includes any tracking parameters.
Mobile Sitemaps. Mobile sitemaps should be used for content targeted at mobile devices. Mobile information is kept in a separate sitemap file that should not contain any information on nonmobile URLs. Google supports nonmobile markup, XHTML mobile profile, WML (WAP 1.2) and cHTML. Details on the mobile sitemap format can be found here: https://supportgoosk.com/webmasters/answer/34648.
Video Sitemaps. Including information on your videos in your sitemap file will increase their chances of being discovered by search engines. Google supports the following video formats: .mpg, .mpeg, .mp4, .m4v, .mov, .wmv, .asf, .avi, .ra, .ram, .rm, „fly, and .swf. You can see the specification on how to implement video sitemap entries here: https://supportgoogle.com/webmasters/answer/80472.
Image Sitemaps. You can increase visibility for your images by listing them in your sitemap file. For each URL you list in your sitemap file, you can also list the images that appear on those pages. You can list up to 1,000 images per page. Specialized image tags are associated with the URL. The details of the format of these tags are on this page: https://supportgoogle.com/webmasterslanswer/178636.