A "one horse town" is a place which relies on a single industry as its major source of revenue -- jobs, the commerce jobs bring, and etc. Et cetera being real estate/land, housing with or without municipal services, one physical bank, a number of churches, a post office, and grocery. One horse -- say mining, "the plant", back office for a large corporation, an exit on the interstate -- will do, as will agriculture, farm goods processing, etc. "Place" can have a large or small population. This creates a culture.