Voltaire was part of an international network of intellectuals dedicated to the principles of the Enlightenment who maintained contact with each other via correspondence.
The Digital Humanities Center at Stanford University, with generous support from the Office of Digital Humanities within the National Endowment for the Humanities, has created a magnificent website Mapping the Republic of Letters that is useful for both research and pedagogy.
On the home page, if you click on Case Studies, a list of philosophes that they have already mapped appears. Click on the Voltaire icon, and you will be directed to an absolutely fascinating set of maps and charts detailing Voltaire’s relationship with his peers. Make sure to scroll down all the way to find the spider chart on the links that Voltaire shared with Benjamin Franklin. While Voltaire and Franklin did not exchange letters, they shared numerous correspondents.
I have seen the Stanford team present their site and some of their research results. Amazing!