From The Washington Post:

"Savanna theory of happiness" - people who live in more densely populated areas tend to report less satisfaction with their life overall.

"Our ancestors lived as hunter–gatherers in small bands of about 150 individuals". Take a brain evolved for that environment, plop it into today's Manhattan, and you can see how you'd get some evolutionary friction.

"The higher the population density of the immediate environment, the less happy" the survey respondents said they were. Second, they find that the more social interactions with close friends a person has, the greater their self-reported happiness.

But there was one big exception. For more intelligent people, these correlations were diminished or even reversed.

Survey: "When high-IQ individuals spend more time with their friends, it makes them less happy."

"Urban-rural happiness gradient" - "Residents of rural areas and small towns are happier than those in suburbs, who in turn are happier than those in small central cities, who in turn are happier than those in large central cities."

References:

Why smart people are better off with fewer friends http://buff.ly/1ZoqBEm
Why smart people tend to be loners http://buff.ly/1q007Nk
Image source: OpenClipArt.org, public domain.