The city and the metropolis: urban form through multiple fabric assessment in Marseille, France

This paper presents a multi-scale detection of urban fabric types through Multiple Fabric Assessment in Marseille, France's second city. MFA is a computer-aided streetscape-based urban morphometric protocol for morphological regionalization of large urban areas. First presented at ISUF 2017, MFA has already been successfully applied to the metropolitan areas of the French Riviera, Osaka and Brussels. The protocol is first applied to the central city, and then to the much larger metropolitan area around Marseille and Aix-en-Provence, stretching over 7000 km2 and home to 2.6 million inhabitants. In both cases, MFA detects eight well-defined families of urban fabrics with clear morphological specificities. The change of spatial extent has nevertheless consequences on the analysis results. On the one hand, urban fabric types detected at the two scales show a precise pattern of correspondences. On the other, each scale allows a finer description of its most preponderant morphological regions, detecting more specific types which are bundled together at the other scale. This is the case for the traditional urban fabrics of the compact city at the municipal scale, and for the suburban fabrics at the metropolitan scale. Accepting some generalisation, the urban fabric types detected by MFA are able to account for the variety of urban forms identified in 36 urban fragments by Marseille's metropolitan planning agency through classical morphological analysis. Beyond the different grain of the analyses (streetscapes vs urban blocks), expert-based and computer-aided classifications are in good agreement. Allowing comprehensive multiscale analyses of urban fabrics for the whole metropolitan area of Marseille, MFA showed the patchwork nature of its 20th century developments and put in perspective the overstated fragmentation of the 19th century urbanisation. Participating to the emerging field of urban morphometrics, MFA opens the way to wider comparative analysis at the national and international levels.