Sitemap rules it follows
A single sitemap file is limited to 50,000 URLs or 50 MB uncompressed. This tool splits it automatically into sitemap-1.xml, sitemap-2.xml and so on, plus a sitemap-index.xml that points to all of them. URLs must be absolute, files must be UTF-8 encoded, and special characters (&, <, >, quotes) are escaped as XML entities. Fragments (#section) are removed because they are not part of the crawled URL, and duplicates are merged.
A sitemap should sit at the root of your site so it covers all paths, and it may only contain URLs from one host.