information in cartography symbols

i am looking for theories and concepts regarding symbols used in cartography.

i have questions like:

many maps present information about quantity by scaling a distinct symbol. obviously this can become a problem when one has to combine different symbols which are in close neighborhood.
wouldn’t it be better to keep the size of an symbol constant but alter instead it’s “decoration” (that is, one could have a simple box, a box with one star, a box with two stars…) ?

cheers from berlin,

jan