Ralph Gentles and five other people spent each summer creating a map of every crack, every depression, every protrusion, every pothole in the sidewalks of New York City. We hear why, and we hear all the things their map does not include. Map making means ignoring everything in the world but the one thing being mapped, whether it's cracks in sidewalks or the homes of Hollywood stars. And, according to cartographer Denis Wood, we live in the Age of Maps: more than 99.9 percent of all the maps that have ever existed have been made in the last 100 years. (4 minutes)