Use X-Robots-Tag HTTP Header to Noindex Indexed Sitemap Files
If sitemap files are indexed for normal search queries, then you can use the X-Robots-Tag HTTP header to noindex all pages ending in .xml or .gz.
Compressing Sitemaps Saves Bandwidth But Doesn’t Reduce Processing Time
Compressing sitemap files using Gzip can save bandwidth but doesn’t impact the speed that Googlebot processes these files.
Check URLs Match Exactly When GSC Reports a URL is Not in a Sitemap
If the URL Inspection tool says a page is indexed but not submitted in the XML sitemap, John recommends checking that the exact URL seen in Search Console is present in the sitemap. For example, you should check that there are no differences with trailing slashes or the case used.
Update Last Modified Date in Sitemap & Use Validate Fix in GSC to Get Pages Crawled Sooner
If technical issues cause pages to show incorrectly (e.g. serving a blank page), you can get Googlebot to crawl these sooner by submitting sitemap files with the last modification date set to when the affected pages were restored. You can also click ‘validate fix’ on pages with errors in Search Console to get Googlebot to recrawl these pages faster.
KML Sitemaps Not Supported by Google
KML sitemaps files are not supported by Google and haven’t been for some years.
Empty Sitemap Files Should Be Removed
Empty sitemap files with no URLs are not problematic for Google but John recommends removing them if they are not needed.
You Don’t Need to Submit Separate Mobile URLs in Sitemaps
URLs for separate mobile sites don’t need to be submitted in their own sitemap. If the rel alternate tags are set up correctly then Google will be able to find these pages through their connection to their desktop equivalents.
Google Have Removed Their Public URL Submission Feature
Google’s public URL submission tool has been removed but URLs can still be submitted through Search Console and sitemaps.
Image Sitemaps Associate Images With Pages But Don’t Provide Context For Images
Image sitemaps are useful for Google as they show what images are associated with what landing pages, but they don’t provide context about the images themselves like alt text and image titles do.