Cities have been described in many ways. They've been compared to bustling ants' nests and trees, and likened to computers with complex networks of intersecting technologies. But Shannon Mattern, a social anthropologist at New York's New School for Social Research thinks we should be wary of the city-as-computer. Her new book, A City is Not a Computer: Other Urban Intelligences, argues that cities are inherently messy creations — home to things, places and people who are allowed to not compute.