It may be possible to predict the average weight of people in a particular district - simply by looking at an aerial photo.
'Walking' neighbourhoods could be healthier
US scientists have suggested that people who live in a "sprawling" district - where shops and services are widely spaced - tend to weigh more.
People living in "compact" neighbourhoods weighed less.
The researchers say this is because people are more likely to try to reach destinations on foot - and burn off calories in the process.
The research, published in the American Journal of Health Promotion, looked at health information from 200,000 people living in 448 US counties and 83 metropolitan areas.
Even when factors such as the average age, social status and wealth were taken into account, they found that residents of compact counties, where shops and offices were reachable on foot, tended to spend much more of their time walking.
Perhaps as a result they tended to weigh, on average, six pounds less than residents of "sprawling" counties.
This may be because these people are more likely to hop in the car to get wherever they are going.
The most "compact" areas were certain New York boroughs, San Francisco county and Hudson county in New Jersey.
Obesity is a rising problem in the US and most of the western world.
It is fuelled not only by high-calorie diets, but also a lack of exercise. In the US, 300,000 premature deaths a year are blamed on excess weight and physical inactivity.
Dr Reid Ewing, from the National Center for Smart Growth, said neighbourhoods could be designed to make them healthier by encouraging residents to do more walking.
He said: "Poor accessibility is the common denominator of urban sprawl - nothing is within easy walking distance of anything else."
The findings are not completely clear, however, and the researchers say that it is hard to define exactly what qualities turn a sprawling neighbourhood into a compact one.
The study appears to be backed up by a separate study, published in the same journal, which measured the number of steps taken by older women in different types of neighbourhood.
Study participants, with the average age of 74, wore pedometers to measure exactly how much walking they did in an average day.
Those who lived near biking or walking trails managed on average 6,797 steps a day, versus 4,908 by those who did not live by such a facility.
Those living within walking distance of shopping areas tended to show a similar difference compared with those who did not.