Data source(s) used: Istat, Administrative units boundaries and territorial bases: Istat disseminates all yearly based data (starting from 2002) of administrative units boundaries for statistical purposes, with reference to the 1 of January for each year. The only temporal exceptions concern the data of the census years (1991, 2001 and 2011) released on the date of the census. The boundaries of administrative units for statistical purposes consist of four hierarchical levels (geographical breakdowns, regions, provinces and municipalities) with national coverage; for the census years the special areas (areas in dispute and administrative islands) are also reported.ISPRA Report on hydrogeological disruption: The Report on hydrogeological disruption in Italy provides the updated reference framework on the danger to landslides and floods throughout the country. The Report updates the national maps of the landslide hazard of the Hydrogeological Structure Plans (PAI) and of the hydraulic hazard according to the Scenarios of Legislative Decree 49/2010 (implementation of the 2007/60 / EC Floods Directive), implemented by ISPRA through the harmonization and the mosaic of the areas bordered by the River Basin Authority.
Other data characteristics: The national total area can be different in years due to the rounding off in the calculation method and the reference census base.As fa as ISPRA data are concerned, the areas with high hydraulic hazard P3 with return times between 20 and 50 years are not available for the territory of the former Regional Authority of Marche Region. The low P1 hydraulic hazard areas are not available for the territory of the former Marche Regional Basin Authority, former Conca-Marecchia Basin Authority and former Authority of the Romagnoli Regional Basins with the exception of the coastal marine areas, and for the irrigation network and reclamation of the territory of the Po basin falling within the Emilia-Romagna Region.Such situation are marked with flag u