The Other Paris is a historical overview of the not-fashionable, not royal parts of the city. It’s a story about the working classes, the poor, the marginalized groups (like the Roma), prostitutes, thieves, political radicals, and more. It is the gritty side of Paris, from when it was a home to everyone of all social classes.
Luc Sante makes a very good, implicit case that it’s these classes that bring life and vitality to Paris, and cities in general. You don’t get vibrant and relevant culture and art and life without people from up and down the social ladder. Paris, and all cities, need everyone, not just the rich and pretty.