Characterizing the 3-D urban morphology transformation to understand urban-form dynamics: A case study of Austin, Texas, USA

Since the 1990s, new urbanism and smart growth have been advocated in the United States, which promote compact urban forms to cope with the environmental and ecological problems caused by urban sprawl. However, there is no uniformity in terms of the spatiotemporal characterization of urban forms. Lack of detailed 3-D urban landscape information makes it difficult to evaluate urbanization trajectories. In this study, we focused on Austin, Texas, U.S., an area with the highest urbanization and the best ranked standard of living, to characterize its evolution of urban morphology and the transformations between urban morphology types (UMTs) over time. We first proposed a conceptual framework to study the UMT transition and urbanization process. Then, the UMT in 2006, 2011 and 2016 was mapped using a synthesis of data sources, which enables a comprehensive understanding of the urbanization process with analytical methods, considering intensification, sprawling expansion, and efficient expansion. Results indicate that Lidar facilitates the multidimensional characterization of urban morphology and its transformation between 2006 and 2016, as maps of UMT were in conformity with the building features of the study area. The urban expansion analysis in different periods (1992-2001, 2001-2006, 2006-2011, and 2011-2016) showed that there has been considerable intensification and efficient expansion after 2000, indicating the increasingly important role of compact development. In spite of the plans and policies on urban development since the 2000s, we found that there was more sprawl than intensification and efficient expansion. This study demonstrates the advantage of applying Lidar data to characterize urban 3-D morphology and understand its dynamics, which helps develop a comprehensive understanding of the urbanization process and provides a tool for planning intentions and policies evaluation on urban development over time.