A new index shows that "more than half of renter households in metro areas across the US experience at least one indicator of housing insecurity..."

If the Danish city of Copenhagen cut air pollution in a massive way, city residents could be living a year longer by 2040.

Urban expansion could claim more than 70,000 square miles of natural habitat by 2030. The US, Brazil, Nigeria, and China will be the big losers.

Zip code remains the biggest predictor of how people define their community, but research suggests these two other subjective factors also matter.