Biography Wikipedia
Wikipedia:
A metroplex is a contiguous metropolitan area that has more than one principal anchor city of near equal importance.
It is this "near equal" importance that makes cities such as Tokyo, Mexico City, New York, Los Angeles, Houston, Chicago, and Phoenix not metroplexes, though they do have secondary anchor cities in their metropolitan areas.
Examples
Japan
Osaka-KobeUnited Arab Emirates
Dubai-SharjahUnited States
In the United States, the term "Metroplex" is most often used to refer to the Dallas–Fort Worth area. Other areas in the U.S. that may locally be called a "metroplex" are:
Baltimore-Washington, Maryland/District of ColumbiaRaleigh-Durham-Chapel Hill, North Carolina, more often called "The Triangle"Gulfport-Biloxi, MississippiMiami-Fort LauderdaleMinneapolis-Saint Paul, Minnesota, more often called the "Twin Cities"San Jose-San Francisco, CaliforniaTampa-St. Petersburg, FloridaWinston-Salem - Greensboro - High Point, North Carolina, more often called the "Piedmont Triad"