But these "informal cities," as they call them, are packed with people, with energy, with established economies, and vibrant cultures—but often hidden from the world around them. To some, these areas are the slums to be avoided.
And while many of these informal cities forge a path to survival in the shadows of the metropolises that surround them, they are in danger from a creeping force of climate change—sea-level rise.
"They tend to settle in these relatively precarious locations, low-lying areas prone to flooding," says Penabad, an associate professor in the University of Miami's School of Architecture.
"They are among the most vulnerable of populations," she says. "We felt that by mapping these locations we would help determine what are the realities of the place, and what is working and what is not working."