Mean density map for the Italian region by GIS techniques

The knowledge of the mean density of the masses between the Earth’ s surface and the geoid (”topographic masses”) is remarkably interesting for several geodetic and geophysical investigations; for this purpose, it is very useful to manage these data in digital form. At present the only information available about the mean density of the Italian region is the 1: 1 000 000 scale graphical map, published by Vecchia in 1955. This map was drawn by computing the mean densities based on many geological maps and profiles, and grouping these values into 8 classes ranging from 1.8 and 3.4 g/cm3, each class being 0.2 g/cm3 wide. By first scanning the graphical map, the raster file was then georeferenced in the WGS84 reference frame, taking special care to modelling and removing the deformations due both to the paper and the scanning process. Finally, ASCII files of the mean density values sampled on a 15″ x 20″ (latitude x longitude) regular grid and a vector file for convenient data manipulation and representation were produced. The main steps of the data processing were performed in the Intergraph MGE environment and a Fortran 77 service program was written in order to I produce the ASCII files in a suitable form.