Retirement is a new phase of life, and, for many, a chance to consider new surroundings. Here is our new list of top U.S. cities for retirement. Data we sifted included housing and living costs, taxes, weather and air quality, crime rates, doctor availability, and active-lifestyle rankings for walkability, bicycling and volunteering. We also looked at economic data with an eye toward a "working" retirement. A fuller explanation of these factors can be found here.