Urbanized areas contain 50 000 or more people while urban clusters have 2 500 to 50 000 people. The 71.2% figure I presented is for urbanised areas, i.e. 50 000+; including the 2 500 - 50 000 urban clusters it rises to 80.7%.

>"Maybe a few hundred thousand tops live in what you might characterize as a real city"

Manhattan alone contains 1.6 million people; your few hundred thousand tops estimate for the U.S. urban population is very short.