Understanding urban expansion combining macro patterns and micro dynamics in three Southeast Asian megacities.

Rapid urbanization accelerates urban expansion, especially in populous areas, such as Southeast Asia. The urban forms and changes at the macro level and the dynamics at the patch level are interrelated. Considering its spatiotemporal interdependences and global-local interactions, we propose a framework to quantify urban expansion by combining macro patterns and micro dynamics. Taking three Southeast Asian megacities, Bangkok, Ho Chi Minh City (HCMC), and Manila, as examples, we calculate the urban land densities in concentric rings (macro pattern) and the proximity expansion index (PEI) of new urban patches (micro dynamic) to compare the urban form changes and expansion patterns based on Landsat imagery in 1990, 2000, and 2014. The results show that the urban form changes have close relationships with the local urban patch dynamics. The macro- and micro-level results in Bangkok and Ho Chi Minh City are interrelated and consistent and the explainable inconsistent results in Manila further reveal the necessity of combination of two scopes. The three megacities developed in different manners, thereby resulting in diverse urban forms and changes. Other methods and technologies combining macro and micro perspectives are encouraged to better understand urban expansion.