Towards sustainability? Analyzing changing urban form patterns in the United States, Europe, and China.

Urban form characterizes the spatial structure of fixed elements within a city, which affects daily life and has significant influence on environmental sustainability. Measuring the spatiotemporal characteristics of an urban form and its relationship with sustainable development is the basis of urban planning. Taking 27 large cities in the United States, Europe and China as examples, we developed a ternary graph to quantify urban forms based on the density distribution of the built-up area. The urban forms were divided into the following classes: central-compact, central-sprawl, decentralized-compact, and decentralized-sprawl. Spatially, the cities in the three regions have experienced rapid urban growth, while the urban forms vary greatly from region to region. Urban forms are dominated by decentralized-sprawl in the United States, and central-compact in Europe and China. Temporally, approximately 80% of sample cities kept the urban form class both in 1990-2000 and 2000-2014. It is noted that 40% of sample cities in China tended to grow in a more sprawling pattern in 2000-2014 than in 1990-2000. From the land-saving aspect of urban sustainable development, compact and central spatial growth can significantly reduce per capita land consumption. Population density decreases in all sample cities, but compact and central spatial growth slowed the rate of population density reduction.