The Sitemap Index
Breaking up the Google Sitemap, or the News Sitemap, into multiple documents is a task that The Permalinks Cascade carries out automatically as soon as you include in the sitemap more than one type of content (Posts, Pages, Categories, etc.), or when the included web pages have images or videos attached – alongside the standard Google Sitemaps, The Permalinks Cascade is able to produce stand-alone Image and Video Sitemaps.
The break up of an XML Sitemap is always accompanied by the creation of a Sitemap Index, a document from where the whole set of sitemaps can be located.
The Sitemap Index
A Sitemap Index is a document collecting all the URLs of the sitemaps in which a single Google Sitemap, or News Sitemap, has been split, and can link to up to 50k sitemaps. Such a document makes submitting to Google changes made to one or more sitemaps a straightforward operation, since just one ping is needed.
The Permalinks Cascade has the ability to automatically switch between single to multi-sitemap mode by keeping unchanged the location of the main sitemap, that way you won't need to submit a new URL through the Google Search Console.
Content Types as Key to Organisation
Keeping sitemaps organised isn't just a matter of personal taste, but can really help you in noticing if something is going the wrong way. That's why The Permalinks Cascade creates a separate sitemap for each type of content, by further splitting the sitemaps when the amount of permalinks for that content type is really generous, so as to actually create groups of sitemaps.
Controlling Sitemap's Capacity
Although The Permalinks Cascade is completely autonomous in creating and managing multiple sitemaps, you have however control on the limit about the number of permalinks each Google Sitemap, or News Sitemap, must contain: you can unhide this setting by clicking on the 'Configure' buttons in the plugin's dashboard.
At the time of writing, The Permalinks Cascade can be set up to generate News Sitemaps listing up to 1k URLs each and Google Sitemaps with a maximum capacity of 10k permalinks each.