Compact Urban Form and Expansion Pattern Slow Down the Decline in Urban Densities: A Global Perspective

The faster growth rate of urban land than population results in the persistent decline in urban densities over time, increasing the cost of land in urbanization. We attempt to quantify influences of urban form and expansion pattern on the decline in densities in 200 global cities. We use openness and proximity to represent the fragmentation and compactness of built-up areas and collect proportions of expansion in three patterns (infill, extension, and leapfrog expansion). We first use correlation analysis to identify significant explanatory variables and then build regression models with the annual change rate of densities as the dependent variable. During two periods (1990–2000 and 2000–2014), urban form and expansion pattern can explain 1/3 variance of density changes. A one standard deviation increase in openness accelerates the decline in densities by 44 %–52 %. A one standard deviation increase in the proportion of infill expansion slows down its decline by 38 %–40 %, but extension expansion accelerates its decline by 20 %–27 %. We further build regression models in five world sub-regions and four groups of different-sized cities, and results verify the stable and robust influences of urban form and expansion pattern. We conclude that compact urban form and expansion pattern can slow down the decline in density. Land-use policies supporting compact growth are encouraged to slow down the decline in urban densities, particularly in fast urbanizing populous regions.