Canonicals Are Chosen by Google Using XML Sitemap URLs
XML sitemap URLs are used to help inform Google’s decision on which URL is chosen to be the canonical.
Make Sure There is a Clear Connection Between Your Mobile & Desktop Sites
It’s possible to include m. pages in your main sitemap file to help Google discover and crawl them for mobile-first, but if there is a clear connection between the desktop and mobile sites then this won’t be necessary.
Crawl Frequency Attribute in XML Sitemaps Doesn’t Impact Crawl Rate
Google takes no notice of the crawl frequency attribute in XML sitemaps or any priority set. Only the last modification timestamp will impact crawl rate.
Google Uses Scheduler to Determine Recrawl Date
Google uses a scheduler before crawling to work out when they need to recrawl URLs. Google will increase crawl rate if it gets signals that it needs to do so e.g. updated modification date in sitemaps and internal linking (especially from the homepage).
New Search Console Will Show More Sitemap Data
The new Search Console will show more detailed information regarding sitemaps and more detail per sitemap file.
Use Several Smaller Sitemaps to Locate Indexing Issues
Having several smaller sitemaps for the different sections of your site is recommended for diagnosing indexing issues.
URLs in Sitemaps Are Not Guaranteed to be Indexed
Google may choose not to index URLs in sitemaps that are very similar to ones already being indexed and if they differ to the ones linked within the site (e.g. trailing slash/non-trailing slash).
Mixed Migrations May Cause Google to Index HTTP or HTTPS URLs
Forgetting to update your sitemap files following a HTTPS migration could cause some pages to be indexed with the HTTP URL and some HTTPS.
Video Sitemaps Can Specify Countries Where Content is Available
With a video sitemap you can define which countries your content is available, which is used for video search results.