Forme di urbanizzazione

Estimating the density of urban settlements by now is fundamental, if not even a priority for urban planning, especially with regard to the phenomenon of urban shrinkage (Haase et al., 2014) , due to t he progressive abandonment , the depopulation and the disuse of t he city centers in favor of consumption of new soil in suburbs and periurban areas (Kabisch e Haase, 2011). For the purpose of analysing the urban landscape in its various forms, the ur ban area, is considered the part of the territory that lies within the administrative municipal boundary. This approach, if on one hand allows a temporal comparison of the different indicators, on the other hand, it does not allow to compare urban structures that are beyond administrative boundaries for the same time period (Munafò et a l. , 2016). The expansion of sealed surfaces within the urban areas occurs mainly in t he suburbs and is characterized by both, the construction of new districts or residential zones (Indovina, 2005; Munafò et al., 2011), and the well -known phenomenon of urban sprawl, that is , low density widespread settlements reaching from the center to the outskirt, concentrated in belts at a distance from about 5 to 10 kilometers from the city center with an increasing growth rate over the last years ( Munafò et al . , 2015).