They put a ton of work into it, and then left it open for random edits. It now has so many placemarks that Google automatically broke it into two pages, which to me defeats the purpose of giving an overview. And I haven't found any way to change the order of the placemarks [hang on-- you can drag the icon in the sidebar!], so I've resigned myself to doing that kind of editing offline in a text editor with the KML files... which is vastly more difficult. [maybe unnecessary?]
GoogleMaps has been switching to a 'new' interface, that doesn't (yet?) allow KML import, so my learning experiments have had to take place entirely within the old interface, which is still available as an alternative (for now?). If you screw up the KML formatting at any point in your hand editing, you'll just get a blind error message when you import, so it'll be up to you to test-modify-repeat until you spot the problem.
But once you've mastered this 'import' command, it's pretty easy to start modifying very simple maps, one tiny step at a time, to learn the basics.
So my plan is to gradually build a map for each episode, getting the sequence right offline, and then when the order is right, edit it in the new interface to add graphic bells and whistles.
Most episodes show Bloom and/or Stephen following a path that can be precisely mapped as a line, with placemarks along the way for Dublin 'street furniture'. Boston College annotates these with useful "What's There Now" notes, too. (The annotations have html-editing available, but this seems very messy to modify by hand, so I plan to stay with plain text as long as possible.)
But as the characters walk, they also think of places they've been in the past, or have read about, and these can also be included in the sequence of placemarks... though this may prove too messy?
BC tries to use human-outline icons to map people's locations as well, which seems overambitious to me, cluttering the main map, but it could be done in separate maps, tracing important characters' paths through the book.
GoogleMaps' KML doesn't mind if imported files use the same 'style' for multiple placemarks, but it seems to immediately duplicate that style so they'll all have a different style number.
Calypso maybe needs separate 'layers' for the neighborhood, the city, the country, and the world. (I haven't found the 'zoom here' command in the new interface [best workaround: hit the "+" button 6ish times to zoom in first, and then select a placemark from the table to focus.)