Over the last century and a half, as the world's metropolises have become more crowded and expansive, underground mass transit systems, commonly known as subways or metros, have become an urban necessity. Ever since the first underground rail line was built in London exactly 150 years ago, maps of these sprawling tunnel networks have evolved with and responded to their social and historical context in creative ways. I trace the historical origins and evolution of these maps, compare their common purposes and features across time and place, and examine the power they have to influence our conceptions of space and human behavior. As the world's population continues its urban migration in the 21st century, subway maps will become an even more integral part of the urban psyche that provides a guiding light in an otherwise dark and frightening underworld.
