The main purpose of this study is to objectively assess how changes in the built environment over time influence physical activity and obesity. The research will focus on collecting and analyzing data related to communities that are being developed or retrofitted in ways that should be more favorable for physical activity and encourages less obesity. This study is significantly different from others in this field in that it will be conducted over an extended period of time (1 year), thus allowing the researchers to determine the associations between changes in the built environment and physical activity, whereas the majority of other studies have focused on existing relationships.