To whom does the "other half" in the title refer? why do you think riis uses this phrase?

"The other half" was a book written by Jacob Riis, a denmark photographer, who worked as a police reporter. He started with photographs as a pastime.

In the book, he highlights the living conditions in the slums of New York City. He used those images and described them.

The title of the book refers to that "half of the world does not know how the other half lives". In Riis book, he explained that workers were paid only some cents a day, children worked a lot, the system of tenement housing.

"The other half" are those who belong to upper classes, who don't experience such living conditions.