Horizontal vs vertical growth: Understanding latent patterns of urban expansion in large metropolitan regions.

Building activity at the metropolitan scale reflects socioeconomic transformations increasingly dependent on place-specific factors. The present study investigates height profile and age of buildings over 12 time intervals (1910s-2010s) in Greece, a country experiencing particularly complex urban cycles in the last century, with the aim to identify distinctive forces fueling vertical and horizontal urban expansion. To discriminate vertical from horizontal expansion, a new indicator of urban growth ('Vertical-to-Horizontal Growth' ratio, VHG) was proposed and used to identify the dominant socioeconomic profile underlying local-scale urbanization processes. Results of this study contribute to discriminate intense vertical expansion coinciding with population growth in large urban areas (Athens, Salonika, Iraklio) from moderate horizontal expansion around medium-rank cities, along coastal areas and in internal lowlands with small compact towns. Greek municipalities display spatial patterns of building activity that reflect the distinct impact of geographical gradients, divergent responses to market stimuli and planning constraints. As in other European countries, urban cycles in Greece were heterogeneous over space, justifying a joint analysis of intensity and spatial direction of metropolitan growth.