Italian geodetic reference systems. Definition and cartographic use

The widespread adoption of standardized Coordinate Reference System (CRS) codifications, particularly EPSG (European Petroleum Survey Group, EPSG, 2026) codes, has greatly facilitated the interoperability of geospatial data within GIS environments. However, these codifications were originally conceived for cartographic applications and may exhibit limitations when used in high-precision geodetic contexts. After a general introduction on the definition of reference systems/frames that are used in Italy, this paper analyses the intrinsic constraints of generic CRS definitions—such as EPSG:4326, EPSG, 2026—and the implications of default datum transformation strategies implemented in common GIS software. A specific focus is devoted to the Italian framework, examining transformations between WGS84 and RDN2008 and the official procedures provided by the Istituto Geografico Militare (IGM) through the VertoX software and grid-based methods. Experimental tests comparing transformations performed in QGIS using official NTV2 grids with those obtained via Verto Online reveal discrepancies at the millimetre level. Although negligible for most applications, such differences may become significant in high-precision geodetic and geodynamic studies, highlighting the need for rigorous CRS management in GIS workflows.