Introduction

More than 55 per cent of the world’s population now lives in urban regions (United Nations, 2018). In particular, urbanization has rapidly increased in low- and middle-income countries in Asia and Africa, sometimes more than three or four times in the last 50 years (ibid). This increase in urbanisation has been accompanied by a simultaneous expansion of the spatial footprint of cities and urban regions. Advances in geo-spatial technology have enabled urban researchers to demonstrate the expansion in the spatial extent of urbanisation beyond what is captured by population data alone. This recent work demonstrates that the rate of increase in land being occupied by cities is greater than the increase in population in most regions of the world (Angel et al., 2016; Seto et al., 2011). The expansion of the spatial footprint of urban regions is therefore more than can be attributed only to population increase. Researchers have attempted to understand and explain this by proposing a range of theories about the nature of urban expansion in different parts of the world, including those that highlight the continuity between urban and rural built forms in different ways (McGee, 2014; Brenner and Schmid, 2011), or those in India highlighting the expansion of urban centres beyond metropolitan areas (Denis et al., 2012).