I don't think a lot of people understand what a metroplex is. A Metroplex is a metropolitan area that consists of 2 or more cities and heavily populated neighboring cities. Dallas - Fort Worth (- Arlington) is the name of a large metropolitan that consists of close to 50 cities. So when someone in Frisco for instance says they live in "Dallas" they indeed do live in the "Dallas - Ft worth" Metroplex, in short, Dallas. For reference to Dallas the individual city, you say Dallas proper.