I'd imagine ithlep is talking about making a database that stores an ID for every citizen along with other personal information like their name, address, those sorts of things. Something possibly...

I would imagine storing it somewhere would be faster since it wouldn't require a whole scan/count.

Not to push the RDM product line too much but http://docs.raima.com/rdms/8_2/Content/UG/Chapter15.htm does provide an overview of replication and how it can be used.