# ADAfinder Tool Applied to EGMS Data for the Structural Health Monitoring of Urban Settlements
## 4 Discussion  
In this section, potential and limitations of the proposed methodology for deformations/structural monitoring of urban settlements are discussed. First of all, regarding the \(ESRI\)_shapefile_ containing the buildings plans, it is worth noting that _OpenStreetMap_ constitutes a convenient service, free and open, for users worldwide. Nevertheless, the provided shapefiles are manually created by a community of contributing mappers, so may contain approximations or imprecisions. By improving the accuracy of the input \(ESRI\)_shapefile_ containing the buildings plans, the accuracy of the results could also increase. If geometrical reliefs of the area are available, they can be included in the procedure. The ADAfinder tool has been applied to datasets of PSs subjected to pre-processing operations. This kind of application somewhat departs from the original use of the tool because the aim is different, since it is focuses only on the buildings. In fact, in the cited applications (e.g., [PERSON] et al. [35]), the input PSs dataset is usually referred to an entire area, without any pre-selection. Then, the identified ADA refers to any part of the area under monitoring. In this work, instead, the structure of the desired results is opportunely channeled, in order to obtain information related to the buildings, and, in particular, to each building affected by deformations exceeding the imposed velocity threshold. The final maps of the vertical and E-W velocity components contain one value for each \"active building\". On one hand, this could appear simplistic, giving limited information. On the other hand, considering the great dimensions of the areas where the proposed methodology could be applied, that could be districts, municipalities, towns, these final synthetic maps give precious preliminary information about the most critical buildings of the area. From a structural engineering point of view, it is important to investigate the two components of deformations, since they can induce different structural response in the buildings, with different levels of hazard. This theme has been deeply studied by [PERSON] et al. [45]. Moreover, it is worth highlighting that the resolution of the Sentinel-1 data is not sufficient to perform detailed analysis at the scale of single buildings. Then, the component velocity maps could be used as a preliminary tool to identify buildings that are affected by significant deformations and need to be further investigated. Some of the possible investigation strategies to carry out are only briefly cited in this work, since they fall outside of its scope. For example, surveys to ascertain the conditions of these buildings could be done, and, if necessary, on-site monitoring could be provided. If other kind of satellite data, with higher resolution with respect to the Sentinel-1, are available, it is also possible to integrate the procedure by analyzing the critical buildings at single scale adopting other approaches [11; 15]. The procedure can be repeated yearly, every time that the EGMS data are updated. This can guarantee not only a monitoring of the absolute value of the velocity/displacements on the whole time, but also differential comparisons between the velocity for each year, establishing additional thresholds of alert on the maximum acceptable values of variation. The two case study areas have different urbanistic features, concerning the dimensions and distribution of the included buildings. This reflects in the PSs covering, as deeply explained in Section 3.1. The applications show that not all the buildings of the chosen areas are monitorable. In fact, when no PS intersects the building plan, as well as if the building is intersected only by PSs along one single orbit, that building is automatically excluded. The absence of PS should not be interpreted as absence of movement. It could be related to the decorrelation effects [46] that could provide a lack of deformation measurement points.