> For example, my user agent may know where I live and thus show me this place relative to that place—the sort of thing that a web component can’t possibly do.
I didn’t say where I am, I said where I live. I didn’t make the distinction clear enough, but I did mean it. The user agent may know more things that are able to make the map more useful for me.
Web components have been able to do that since before web components existed: https://developer.mozilla.org/en-US/docs/Web/API/Geolocation . It's almost as old as <canvas>.