Cities
The author distinguishes "town" from "city" as the latter is established by a group of noblemen who have large estates, and who seek to live in an "agreeable society" of others of their social class, distant from their land holdings.
Where several such persons live in proximity, they bring with them a sizable retinue, and attract merchants and artisans that seek to serve their houses. While the population that is attracted may also serve one another, the chief source of income of all are the noble houses of the city.
Another distinguishing feature of cities are "workshops and manufactories" whose chief purpose is not the production of raw materials but the transformation of these materials into finished goods for consumption and export. In that way a city draws not only on the wealth of the inhabitants of the area, but upon income from foreign trade. But this considerations are pit aside "so as not to complicate our subject," except to note that great cities often arise on the sea coast, on the banks of great rivers, and in other locations that a conducive to logistics and trade.
The size of a city is reckoned to derive primarily from the number and stature of its noble houses, which are in turn derived from the productive capacity of their land holdings, however remote from the city itself.