The definitive map is this one from the Census. It shows the metro areas by county and you can see where the high density urbanized areas are within the metro areas. Exurbs generally match to metro counties that lack significant urbanized areas, since they would be primarily commuters. I would guess that most people would think of the micropolitan areas as rural with a significant town within the county.
Note that there is no suburban area, and this was a huge struggle with Griffin's work two years ago. Suburban areas evolve and old ones begin to look urban, and older more distant urban centers can become suburbs as a metro area expands. The term is very subjective, so the Census avoids it.
The criteria they use, seems a bit lacking as the Charleston WV shows. Claiming Clay and Boone counties to part of a "metro" is absurd.
