Sitemaps for SEO
Sitemaps are used by Search Engines to figure out which pages of a site they should crawl.
There is a standard XML format for sitemaps.
Google only allows 50k urls per XML file, so if you have more URLs, you need to split the urls into multiple sitemaps. Then you can create a sitemap index file and submit it to Google. Or you can just submit a bunch of sitemaps to Google directly.