San Francisco is the second most dense city in the country, after only New York, and that's a good thing, according to a study that examined urban sprawl and its effects. The study looked at residential and employment density, neighborhood mixes of homes, jobs and services, strength of activity centers and downtowns, and accessibility of the street network. It then assigned a Sprawl Index score to each urban area that it examined, with the highest scores indicating the most density and least sprawl. San Francisco's score of 194.3 put it behind New York's 203.4 but well ahead of its closest follower, Atlantic City, which came in at 150.4 The study also found that residents in denser areas tend to be safer, healthier and live longer than those in more sprawling areas. For every doubling of an index score, life expectancy increased by 4%. Driving rates (and the risk of fatal collision), body mass index, air quality and violent crime all contributed to this difference. Dense areas also provided greater opportunities for economic mobility and more transportation options.
· Measuring Sprawl 2014 [Smart Growth America]