650 Subfield $z - Geographic subdivision:

Subfield $z contains a geographic subject subdivision. Subfield $z is appropriate in field 650 only when a geographic subject subdivision is added to a main term.

Examples:

650 #0$aWorld War, 1939-1945$xCampaigns$zTunisia.

650 #0$aReal property$zMississippi$zTippah County$vMaps.