New spatial dimensions of global cityscapes: Concepts and spatial methods for delineation

Urban areas are ever-increasing, generating a transformation of rural and urban land on a global scale. Today, more than half the world's population live in cities, a figure which the United Nations expect to rise to 66% in the next few decades (UN-DESA, 2015): 6.3 billion people will inhabit urban areas by 2050. This urbanisation process will have environmental and non-environmental effects including resource consumption, topographical changes, climate change, pollution, water quality and availability, increased vehicle use, and socioeconomic as well as political impacts (e.g., Weng, 2014; Schneider et al., 2015; Alqurashi & Kumar, 2016; Wheeler, 2009). Information on human settlements is not just necessary for ongoing population estimation, vulnerability assessment, planning and governance, but also for time-critical applications like emergency response (Florczyk et al., 2016). One of the main issues in urban geography in this context is the question of defining urban areas. What is the best way to delineate urban space? Commonly, administrative boundaries give a name to a place. Often though, these limits do not represent underlying structures which are better explained through other characteristics such as natural regions or ecosystems – for example, topography (e.g. watersheds, valleys) or actual settlement patterns, but also economic, functional and political linkages