Mostly focused on R but I have included it here because of the discussion of the legend.
Particularly improving the focus of the information presented.
I rarely want all the information about a subject.
I just want the information that is helpful in my particular context.
A topic map may hold far more information that it ever displays to me.
And only display some small part of that information.
Otherwise it is like drinking from a news sewer (insert your favorite example) during a disaster.
Lots of information, little of it makes any sense.