Currently researching the content at https://developers.google.com/search/docs/guides/search-features to gain a better understanding of Google Search. The text below is a map of their content and my interpretations of it and how I can apply certain measures on my own sites and client projects to ensure they get the best exposure possible.
Types of URLs you provide
If you want to provide information updates about your URLs and establish relationships between them and alternate URLs, it might make sense to use an XML sitemap, which can list both canonical and alternate URLs in one file and provide modification dates.
The following example shows a simple XML sitemap with a single page entry that uses both canonical and AMP URLs, and establishes a modification date.
<?xml version="1.0" encoding="utf-8"?> <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"> <url> <loc>http://example.com/dogs/poodles/poodle1.html</loc> <xhtml:link rel="amphtml" href="http://example.com/dogs/poodles/poodle1.amp.html"/> <lastmod>2016-01-13T18:30:02Z</lastmod> </url> </urlset>
The timestamp for your date should be in W3C Datetime format. This format allows you to omit the time portion, if desired, and use YYYY-MM-DD.
We recommend that you use either plain text or XML as formats for your sitemap. In addition, a sitemap file can't contain more than 50,000 URLs and must be no larger than 50 MB uncompressed, so you should split large numbers of URLs into multiple files.