The Centre for Diet and Activity Research (CEDAR) [1] is an interdisciplinary Centre of Excellent in Public Health Research, a partnership between the University of Cambridge, the University of East Anglia and MRC Units in Cambridge. It studies influences and interventions on diet and physical-activity behaviours, and helps to shape public-health policy and practice [2]. Among its current research programmes are: ‘Social, economic and neighbourhood determinants of diet’ (which is working to identify and measure social and economic factors influencing food choice, including ‘the ways that food choices and diet quality can vary across physical space and among different groups in society’) [3] and ‘Environmental determinants of physical activity and dietary behaviour’ (using a Global Positioning System and Geographic Information System to study how the local environment influences physical activity and dietary behaviour) [4].