one thing I don't quite know how to formulate (or whether it is sensible at all) is how to find whether a given set of number "bunch" at some location of the number line because of the difficulty introduced by infinite cardinals. for example the harmonic series in [0,1] is countable, but it has a limit point at 0. The cantor set is uncountable, but there are intervals where there are no numbers thus the irrationals are effectively concentrated at the pseudoboundary and the interior.
I am not sure if there's a mathematical quantity that captures this