A nisba links a transmitter to a tribe, locality, occupation or another association. It distinguishes people with identical personal names, but its cause must be established rather than assumed.
Tribal nisba: affiliation with a lineage or tribe.
Geographical nisba: connection to a town or region.
Occupational nisba: association with a craft or profession.
Other affiliations: residence, proximity or a conventional label.
A designation such as al-Baghdādī need not prove that its bearer was born in Baghdad; it might reflect residence or another identifiable link. The researcher must verify what the affiliation denotes in that individual case.