The following is available regarding the connecting Tableau server to the mapping services. (http://kb.tableau.com/articles/issue/maps-do-not-display)
To show online maps, Tableau Server must be able to use the Run As User account to connect to the following two mapping servers over the HTTP port 80:
- mapspatial.tableausoftware.com (accessed the first time the map view is opened after restarting Tableau Server)
- mapvisual2.tableausoftware.com (accessed every time the map view is opened)
I cant find desktop specific information, but would assume given the nature of the desktop environment it would be connecting to the same locations. these will need to be whitelisted on your firewall.