If you could look down from space and see the emotional state of every person in a city, what would it look like? We don’t have that technology yet, but Twitter is providing the next best thing. In a new study, researchers harvested every tweet that was geographically tagged to Manhattan and its surrounding boroughs during a 2-week period in April 2012. That was the easy part. The trick was deciphering the emotional content of those 604,000 utterances. Luckily, a large portion of tweets come with emoticons—for example, :) and :( for a smile or frown. By using these tweets as a training set, the team taught a computer to distinguish negative, positive, and neutral emotions. After projecting those emotions as colors on a map of New York City (pictured)—blue for positive, red for negative—the city’s mood landscape was suddenly revealed. Some of the patterns are no surprise. For example, people tended to be happiest near green areas such as Central Park and unhappiest around transportation hubs such as Penn Station and the entrance to the Midtown Tunnel. But the fine-grained details are striking. The closer people were to Times Square, the happier they got. And the city’s mood had a daily rhythm, mirroring that of the individuals who live and work there. People’s feelings—both positive and negative—were muted in the morning and peaked around midnight. The happiest place in Manhattan was Fort Tryon Park; the location is way uptown and thus takes effort to get to—the kind of effort people make when they're enjoying a day off. The saddest? Hunter College High School. No surprise there. The data were collected the week students returned from vacation.