Nature and urban structure: The United States vs European Union

Background/Question/Methods

Interwoven within urban matrix are undeveloped, recreational, and green spaces, yet the abundance and role of these interstitial ecosystems, and the broader environmental, is often overlooked in the current theory of urban structure and growth.  Our objective was to compare the power law scaling properties of land covers in cities on two continents, the United States and European Union. Power law scaling (A = αx^β) has been used in biology, physics, and urban studies to understand a system’s underlying processes.  Here we used power law scaling properties (specifically the slope (β), breakpoints, and residuals) to investigate 1) the differences in urban structure and growth in the US and EU, and 2) the role of interstitial ecosystems, climate, and topography on those patterns. Scaling properties were calculated based on a large population range (2500 to 12 million) which resulted in 3592 US and 8204 EU cities.  We calculated for each city the total area of a contiguous city, area of land uses, population, precipitation, and topographic slope based on publically available GIS data (ex. 2011 NLCD, 2010 EU Urban Atlas).   

Results/Conclusions

Results show that urban structure and the role of nature differs in US and EU cities.  Both the US and EU scaling had significant breakpoints, above which the trajectory of land uses (β) changed.  In the US, above 360,000 people cities β for total area decreased from 0.95 to 0.78, indicating US grow more densely above this threshold.  In the EU, β increased from 0.86 to 0.92 at a population of 220,000, indicating the increase in density actually slows for large EU cities.  Interstitial ecosystems contribute to the differences in density.  In the US, the percentage of undeveloped and open space were maintained, while recreational land and water bodies increased.  EU cities had overall higher density residential development, while the percentage of green space, recreational land, water, and undeveloped land increased as population increased.  In addition, more variation between US cities could be explained by precipitation, whereas in the EU no relationship was observed.  In sum, EU cities are initially much denser than US cities and incorporate “natural” spaces as populations grow, whereas the US starts with high levels then infills with denser urban land covers.