For me, it is Thrilling Cities (1963) by Ian Fleming, who is better known as the creator of James Bond. It is about each of the leading cities Fleming visited and his views on them.
When reading it, you really get a sense of how proper information informed the writing of Bond. For example, he mentions how in Chicago the role of crime had changed, into a more organised labour system.
This is exactly what one of the mafia characters in Goldfinger reveals when explaining his unwillingness to go along with Goldfinger’s plan, saying that the old gangland wars are over and stunts like Goldfinger’s plan to rob Fort Knox, should be a thing of the past.
by LewisKOTyson