Analyzing horizontal and vertical urban expansions in three East Asian megacities with the SS-coMCRF model

A recently proposed method based on the spectral similarity-enhanced Markov chain random field cosimulation (SS-coMCRF) model has provided a practical approach for estimating both horizontal and vertical urban expansion of megacities using Landsat images. Estimating vertical urban growth-the area change of mid-rise or taller buildings (MTBs)-makes it possible to gain some new insights into the urban expansion of megacities. This study makes use of the new approach to examine the horizontal and vertical urban expansion of three capital megacities (Beijing, Seoul, and Tokyo) in East Asia during the late 1980s to the mid-2010s. In contrast to previous studies that only assessed horizontal urban growth, which usually showed almost no increase in urban area in some highly developed cities, this study indicates some different findings: (1) Both horizontal and vertical urban expansion had been happening in the three megacities during the studied period, especially with respect to vertical urban expansion. During the studied period there were 20.7 km(2), 11.3 Km(2), and 6.8 km(2) MTB area increases in Beijing, Seoul, and Tokyo, respectively. (2) Different cities showed some differences in growth patterns, mainly because they were at different urban development stages and impacted by different local situations in terms of geography, population, and development policies. (3) A similarity is that the three megacities all tended to horizontally expand initially and then grow vertically in the already developed areas. This study may provide a useful new perspective on the urban expansion of megacities.