Vertical versus horizontal: theory and practice of urban densification in evolving metropolises

The urban growth, its continuous use of land and the associated problem of soil sealing force urban expansions to search for a sustainable densification. The paper attempts to explore and compare the urban conditions' growth on the fringes of two cities in Asia and Europe - Shenzhen and Vienna - as two opposite realities defining different strategies to control the urban expansion: while Shenzhen use the verticality to create new space, Vienna works on the horizontality and the regeneration, generating a neighbor’s contiguity in the urban areas. The paper discusses and illustrates the two possibilities for dense built environments -horizontality and verticality in the metropolitan form-, as opposite yet possible strategies to achieve dense built environments qualifying urban spaces, infrastructures, buildings. To this aim Hong Kong, and Vienna are compared, to understand differences and attempt at responding to the central research question: Is it possible to identify an optimal urban form? Buildings’ and neighborhood’s typologies have been observed to aim at this understanding. Even though general conclusions cannot be drawn from specific case studies, is the authors' considered opinion that urban textures in the built environments are very much connected with and their successful evolution depends on the strict relation with humans and their activities (working, living, entertaining and dwelling). In this context, appropriate strategies for urban densification, in their different forms, might represent an effective path to meet the new conflicting challenges of sustainability and rapid urban growth.