I don’t know if the US works differently but here in portugal, your remains get exhumed after some time and someone else is buried in the same grave. There’s also a concept of family grave whereby all members of the same family get buried in the same hole (they dig deeper than normal so that 2 or 3 people can be buried on top of eachother)… and still cemeteries are being expanded or new ones are built all the time.
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