Assessing Polycentric Urban Growth through a Mathematic Morphology Approach

The present study introduces an original assessment of polycentric urban growth by applying mathematical morphology to the urbanization-driven landscape transformations in Rome, Italy, between 1949 and 2008. Using Morphological Spatial Pattern Analysis (MSPA), landscape dynamics were assessed at four years (1949, 1974, 1999 and 2008) by analyzing the spatial distribution of seven metrics (core, islet, perforation, edge, loop, bridge and branch) in nine land-use classes. Changes in landscape structure were analyzed through hierarchical clustering applied separately to metrics and land-use classes. While the total class area of natural and especially agricultural land-uses decreased during the investigated time interval owing to urban expansion, the percent 'core' area declined with different rates according to the specific land-use class. Only moderately decreasing rates were observed for urban areas and woodland, while highly negative rates were recorded for all the remaining classes. The average percent change in 'core' areas diverged between the three intervals considered (1949-1974, 1974-1999 and 1999-2008) pointing out the role of different spatial determinants of landscape transformations. Hierarchical clustering results f suggest the increasing complexity of landscape morphology over time and the different time paths for abundant - sometimes expanding - classes (urban areas, urban parks, woodland, arable land) and scarce - generally decreasing and fragmented - classes (crop mosaic, vineyards, olive groves, pastures). Taken together, results indicate that urban settlements expand in a scattered and mainly chaotic way without evidence of polycentric growth. This clearly reflects the progressive 'fractalization' of non-urban landscapes undergoing exurban development without the formation (or consolidation) of sub-centers, a process characterizing polycentric growth.