sensibility or resistibility to electromagnetic impulses, and the type and routing of incoming installations.
Lightning density (or the number Ng of lightning strikes per km2 and per year) is different for different geographic coordinates, in particular for different latitudes, and may be obtained either directly from the data of lightning location and registration systems or indirectly on the basis of isokeraunic level, which is expressed by the number TD of thunderstorm days in a year, using the following relation valid for temperate regions: