While you check your campaign report, you will notice opens by location that displays the location of the subscribers who opened your campaign.
The data is collected by tracking the ip that matches with a location.
Opens by location data accuracy
Basically the data is accurate except in two cases:
Gmail uses its own proxy server with a specific IP in US, which means when a subscriber that has a gmail account opened your campaign his location will be US even if he lives in Italy or in other countries. (E.g: If you have a list of 1,000 subscribers and all of them has a gmail account, so even if their real location is Spain/Italy/Canada....the opens by location will display US location, so don't be surprised, this is something that gmail uses and no email service provider can change it. (It's a part of the Gmail policy).
Due to Apple Privacy, opens by location for apple users might be inaccurate