The extension of the city into the countryside, particularly associated with improvements in mass transport. Torrens (2006) AAAG 96, 2 argues that population growth is one of the most important engines of urban sprawl, and Irwin and Bockstaehl (2002) J. Econ. Geog. 2 think that sprawl may be caused by negative externalities between developments. The implication is that the undeveloped land that is adjacent to sprawl is less valuable in residential use and less likely, ceteris paribus, to be developed residentially in the future. See J. Wolch et al. (2004) on urban sprawl in California, and Glaster and Cutsinger (2007) Urb. Geog. 28, 6 on sprawl and racial segregation. Bartl (2011) Urbaniz. & Water has some interesting thoughts on urban sprawl in Indian cities. See urban containment.