§1. As a rule, a portion of the people of God which constitutes a diocese or other particular church is limited to a definite territory so that it includes all the faithful living in the territory.
§2. Nevertheless, where in the judgment of the supreme authority of the Church it seems advantageous after the conferences of bishops concerned have been heard, particular churches distinguished by the rite of the faithful or some other similar reason can be erected in the same territory.
Source: Code of Canon Law (Vatican.va)