NHK WORLD JAPAN- A TASTE OF TOKYO-Trails to Oishii Tokyo 

You’re both right. Population of Tokyo is 14million. Population of Greater Tokyo Area is 40 million. Looking out of the window on a train ride from Tokyo, through Kawasaki and onto Yokohama there is no indication where Tokyo-to ends and Kanagawa-ken begins.

The idea of a universal sauce was the inspiration, as you know they taste nothing alike !