«Porosity» is a system of various emptiness, passes and spaces in urban fabric. These emptiness define a microclimate, permeability, the total area of open spaces, and so define the quality of urban fabric. The article characterizes the various criteria for evaluation of the intensity of the urban fabric. The article gives the comparison of population density and building density in Russia and abroad. The author shows the main trends of building density. The modern methods of density estimation and efficiency of development are considered. The definitions of «porosity» for describing three-dimensional characteristics of dense development are given. The article describes the influence of porosity on micro-climate, permeability, space consumption, the perception of space. The article also describes the main directions of «urban porosity» research.

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