## 4 Discussion
### CLARA WebGIS Potential and Perspectives  
The knowledge of the spatial distribution of the local seismic amplification effect, of the main characteristics of buildings, and of the soil-building resonance effect contributes efficiently achieving a three-part objective: (i) increasing the seismic resilience of an urban system and reducing the probability of a crisis occurring in the case of an earthquake; (ii) reducing the potential losses in economic and social terms; (iii) facilitating the return of the urban system to pre-existing conditions or recovering a new state of equilibrium by reducing the recovery phase time. If we share the basic principle according to which the use of the areas affected by seismic amplification and their secondary effects (road obstruction, interruption of services, slowdown of rescue services, etc.) should be more carefully regulated, then the mapping of the probability of occurrence of soil-building resonance, along with the consequent assessment of the areas with the greatest probability of increased damage during seismic events becomes crucial for the implementation of mitigation and prevention strategies (urban planning laws, land-use planning, planning for intervention in emergencies and to manage post-earthquake crises). For example, the soil-structure interaction maps in the urban area of cities could help to (i) determine the most suitable areas for urbanization (characterized by low resonance levels) or eligible for other intended uses, such as parks, gardens, recreational areas (characterized by medium/low resonance); (ii) define seismic retrofitting strategies for existing strategic buildings/structures/infrastructures; (iii) integrate microzonation studies with the effects due to the presence of buildings and their interaction with the soil according to a holistic approach [8]. The achievement of the latter two targets is all the more feasible since some governments are currently financing seismic retrofitting for existing buildings and microzonation studies, e.g., the Italian government through the 'Sigma bonus' (Ministerial Decree August 6, 2020, n. 329) [70] and 'Guidelines for Seismic Microzonation' [71] respectively. For years, technical and scientific communities have been discussing the opportunity of creating for each building a certificate containing all available information. Besides basic information on each building (height, age of construction, typology, use, etc.) and geological/geotechnical data of the relative foundation soil, the CLARA WebGIS contains the estimates of the fundamental frequency of all urban soils and the vibrational frequency in the linear elastic domain for 4043 buildings within the urban area. Such information constitutes invaluable knowledge for freelance engineers, as it is key for numerical models of seismic retrofitting. In addition, CLARA WebGIS allows further evaluations in support of mitigation strategies, both on an urban and suburban scale, by combining the geophysical and engineering data contained in the layers. For example, by cross-referencing the data on the state of conservation of buildings with the probability levels of soil-building resonance occurrence, it is possible to estimate the number of buildings for which seismic retrofitting is recommended (Figure 15). The experience gained in the development of the CLARA WebGIS with respect to the creation of a digital surface model (DSM) starting from the elaboration of satellite data, can constitute an adaptable reference for those situations in which there is no availability of open data on building heights. Indeed, if DSMs, which represent the Earth's surface with all the human-made objects on it (including precise information on the orthometric heights of buildings and infrastructure), are accompanied by the orthometric elevation of the topographic surface (provided by a digital terrain or elevation model--a DTM or a DEM), allow retrieving an accurate estimate of the height from ground for each building.