International comparison of observation-specific spatial buffers: Maximizing the ability to estimate physical activity

Lawrence D. Frank, Eric H. Fox, Jared M. Ulmer, James E. Chapman, Suzanne E. Kershaw, James F. Sallis, Terry L. Conway, Ester Cerin, Kelli L. Cain, Marc Adams, Graham R. Smith, Erica Hinckson, Suzanne Mavoa, Lars B. Christiansen, Adriano Akira F Hino, Adalberto A S Lopes, Jasper Schipperijn