edit to add: And this makes a large part of the load time (when not cached). Other than that, the largest part is the SSL handshake and the fact that the server seems to be a bit slow (WRT the fact that it serves static content; 200ms for dynamic stuff would be okay).
Still a lot faster than most of todays websites.
The former is specifically for reducing requests, while the latter is more about UX.
Sure, it's different from the <map> element (which is officially an image map, as you say).
But it's effectively mapping out the sections of a large image that you care about and then using CSS to display parts of it
For css sprites, you could submit an image to a folder in the monorepo, and a couple of minutes later an automated system would update the image with all the sprites, and create constants that you could you in your templates/css to use the icons with the coordinates/size of the image.
(As Deno shows, ESM imports make a lot of sense from CDN-like URLs again. It just won't perform well in the browser because there is no shared cache benefit.)
Same goes back when we could just load a single library from the Google public version (cough-jquery-cough) and then all the on-page JS was just in-tag handlers. Not that it was better but boy howdy was it faster to load.