Question is what determines a family? Is it that they are all living at the same address or that they are part of the family group - mother, father, daughter, son ?
If a child moves away to live / work elsewhere does that become a new family or is he / she still part of the original family but living in a different location?
When someone marries they start a new family - what if there is no marriage but still a partnership possibly with children? What about a child living with grandparents with the main family still intact? I have that several times in my tree - possibly due to space / money. Then there is the son / daughter marrying but living at the same address as the parents - does the spouse join the new family or stay with the original family?
I think that address is one way of determining a "family" group but that requires that the address is recorded for all family members at any particular time - easy for a census but a little more work for an event (e.g. birth or death) plus the assumption that all family members are still at that address at that time - likely for children but not certain as they grow older.
Also the qualification of a location needs to reflect the family - perhaps a Census or a RESI however in my GEDCOM all census entries have a PLAC, all RESI entries have an ADDR but all other "events" also have a PLAC very difficult to differentiate.
What is the saying? More questions than answers! It would be good to get more opinions on this. Could this discussion be moved easily to the Lost Cousins Forum?