Istanbul's Central Business District as the real estate industry refers to it, is not the historic city center, but a 7-km-long north–south corridor of modern areas mostly along Barbaros Boulevard and Büyükdere Avenue.
[1] The Istanbul Metro's Line 2 serves the CBD's main north-south corridor, with Line 6 and Line 7 providing east-west service.
In addition, Line 7 is to be extended southward from Şişli—Mecidiyeköy station to Beşiktaş ferry station.
The historic city center is in Fatih and contains historic sites, the Grand Bazaar and adjacent wholesale/retail districts, but is not a modern "central business district" in that it does not have modern retail formats, dense residential and hotel towers, etc.
These can be found in the following edge cities with concentrations of office space, shopping malls, residential towers, entertainment and educational facilities, hospitals, etc.