How does Malcolm Gladwell use imagery in The Tipping Point?

The book begins with the description of the city of Baltimore in the 90s, a time when an outbreak of syphilis affected the city and its people. The author mentions possible reasons that a new outbreak appeared and while analyzing the contributing factors, he paints Baltimore as being a city populated by promiscuous characters, people of questionable character who through their lifestyle impact in a negative way the life of those who live near them.