Urban expansion in the megacity since 1970s: a case study in Mumbai

Understanding the process of urban expansion in megacities is considerably important. In this study, megacity Mumbai was selected as the study area. Based on the urban maps retrieved from Landsat images in 1973–2018, we mapped and quantified the detailed urban expansion process of Mumbai by adopting the expansion area and speed indices, centroid shift model, urban expansion type method, hot-zone identification method and landscape metrics. The results indicated that: (1) urban land remarkably expanded, and its centroid moved from the southwest to the northeast direction, mainly adopting the edge-expansion form. (2) Distinctly spatiotemporal heterogeneities existed in eight directions, faster in the north, northeast and east directions, whereas slower in the five other directions. (3) The number of hot-zones increased from two to three and moved outward in space from urban centroid. (4) The urban landscape of Mumbai showed the ‘diffusion, aggregation, re-diffusion’ pattern and presented differences in eight directions.