The commercial area of the capital extends from the old Qing River market to the Southern Commons and to the city border on the north. . . . Some famous fabric stores sell exquisite brocade fabric and fine silk, which are unsurpassed elsewhere in the country. . . . Most other cities can only boast of one special product; what makes the capital unique is that it gathers goods from all places. Furthermore, because of the large population and the busy commercial traffic, there is a demand for everything.” Description of Hangzhou, capital of the southern Song dynasty, circa 1235 C. E.

Which of the following assertions in the description of Hangzhou above would be most difficult to verify?