They should be large numbers of more flexibly placed, smaller cities. That way, when change happens, from the inordinate number of ways that change can come from, we will seldom have too many of much of anything in one concentrated area. Better all the way around, if you think about it long enough. One of the reasons I like floating cities.
The Indian government is buying up land to build a futuristic megacity called Amaravati. By 2035, they projected, it would be home to 11 million people and cover 3,322 square miles — ten times the area of New York City.