Socioeconomic analysis of Italy normally sees a distinction between the wealthier, more industrial Northern half (e.g. cities like Milan) and the poorer, more agricultural, mafia-troubled Southern half (e.g. Naples) normally including Sicily and Sardinia too. A rough line for the split could be about the latitude of Rome.

"Italy's boot" here corresponds to this Southern Italy.

https://en.wikipedia.org/wiki/Southern_Italy

http://www.nytimes.com/1996/11/15/world/north-south-divide-i...

Thanks, I wasn't familiar with the expression in that context