SAN FRANCISCO — This city is full of parks that invite exercise, and bike lanes that make commuting a workout. It’s home to social services that tend the poor, and taxpayers who willingly fund them. Smoking is banned at restaurants and bars — as well as in workplaces, at bus stops, throughout public housing, at charity bingo games, and even inside stores that sell tobacco.

These factors might help explain why the poor live longer in the San Francisco area than they do in much of the rest of the country. According to a new study published Monday on how income and geography shape life expectancies, a poor person living in the San Francisco area can expect to live about three years longer than someone making the same income in Detroit. That difference — three years — is equivalent to how much national life expectancies would rise if cancer were eliminated.

“If you think about the cancer comparison, having cancer is not just about having a shorter life. It’s also about having an unhealthier life, a much lower quality of life,’’ said Stanford economist Raj Chetty, the lead author who co-wrote the study, published in the Journal of the American Medical Association, along with seven other economists from the Massachusetts Institute of Technology, Harvard University, the Treasury Department, and McKinsey & Co.

Think about their new data as if the poor in Detroit get cancer and the poor in San Francisco don’t. “Then,’’ Chetty said, “you can see that this is a big deal.’’

The research, based on the tax and Social Security records of everyone in the United States between 1999 and 2014 with a valid Social Security number and earnings, gives the most precise look yet at a pattern that has long troubled health experts: The richer you are in the United States, the longer you live.

But what’s especially striking is that the poor live even shorter lives in some places than others. They have longer life expectancies in affluent, highly educated cities such as San Francisco, New York, and Los Angeles.

Among the 100 largest commuting zones ranked by the researchers, six of the top eight for low-income life expectancies are in California, a state with a strong safety net and a history of regulating where you light your cigarette or what comes from your tailpipe.

The poor live shorter lives in Las Vegas, Louisville, and industrial Midwestern towns such as Gary, Ind. Geography also matters much more for the poor than for the rich.

The health behaviors of the wealthy are similar wherever they live. For the poor, their likelihood of risky behaviors such as smoking depends on geography, on whether they live in a place where smoking is common or where, as in San Francisco, cigarettes have been shunted out of view.

“It is as if the top income percentiles belong to one world of elite, wealthy US adults,’’ Nobel Prize-winning economist Angus Deaton writes in a journal editorial accompanying the new paper, “whereas the bottom income percentiles each belong to separate worlds of poverty, each unhappy and unhealthy in its own way.’’

The study offers the most exhaustive account yet of the rich-poor gap in US life expectancy. The data reveal that life expectancies continuously rise with income in the United States.

For men, the gap between the top and bottom 1 percent nationwide is nearly 15 years. For women, it’s 10 years. And these disparities have widened since 2000. People in the top 5 percent have gained about three years of life expectancy. People at the bottom have gained almost nothing.

The economists don’t have definitive explanations for the relationships they observe between income and health. It’s hard to imagine, for instance, that the richest Americans can buy things that make them healthier that people who are just slightly less rich can’t afford, Harvard economist and coauthor David Cutler said.

But among the poor, the differences in what money can buy likely explain an important part of the longevity gap.

“At some point, it does become causal: You can buy better housing; you can buy better food,’’ Cutler said. “You own a car that actually works, so you can drive to the grocery store more regularly.’’