Ans. “the material artificial Thing, which consists of houses and streets, and has four million inhabitants”;
or else
“the Town which has four million inhabitants.”
[Note that we here use the article “the” instead of “a”, because we happen to know that there is only one such Thing.
The Reader can set himself any number of Examples of this Process, by simply choosing the Name of any common Thing (such as “house,” “tree,” “knife”), making a Definition for it, and then testing his answer by referring to any English Dictionary.]