According to the UN, about 827 million people around the world live in "slums." As Business Insider points out, "slums" is a bit of a fluid term that can mean anything from small downtrodden working-class neighborhoods to whole cities in transition.
BI has pulled together a collection of satellite images showing some of the world's largest slums:
Petare, Venezuela -- 600,000 - 1 million people
Sadr City, Iraq -- approx. 2 million people
Neza-Chalco-Itza barrio, a slum in Mexico City -- approx. 4 million people
Click here to see more images @ Business Insider