Earthman, Come Home: James Blish

Book III of Cities In Flight. When the cities left Earth, they exchanged a simple environment for one of constant, sometimes shattering change. The Universe was littered with cultures in every conceivable stage of development. Only the iron hand of the germamium-backed economy and occasional interventions by the Earth police imposed some kind of order on the space-ways. Even John Amalfi never got used to the constant crisis of life on board 'Okie' city - and he'd been mayor of New York for nearly five hundred years now...Cover art by Chris Foss.