Check reference  : ISOGG 2011
But it could be based on nothing more than a rounding error of the statistics: 4.8% would fall under the lowest limit in the map, 5.2 would fall in the 5-10% range.
Sorry Abe, but it's not as the map itself is based on an earlier work, to whit:
Adapted from S. Rootsi et al. (2004), Phylogeography of Y-Chromosome Haplogroup I Reveals Distinct Domains of Prehistoric Gene Flow in Europe, American Journal of Human Genetics 75, 128–137
Which means that your map is based on a contemporary study to the source I gave. Not that it's a significant difference as most of the percentages given in my source were rounded up, which is not an uncommon occurance. The actual percentages for the three major areas in Sicily were as follows: