In megacities, creativity flourishes on a vast scale

In his new book, “The Human City: Urbanism for the Rest of Us,” author Joel Kotkin — a critic of the recent push for greater density in some American cities — devotes a chapter to the downside of megacities. People streaming in from the countryside, he notes, encounter pollution, limited water supplies, woefully inadequate transportation systems, shoddily constructed housing in ill-governed informal settlements, and “health challenges that recall the degradations of Dickensian London.”