Territorial nexus is a concept in which hai described in Article 245 of the Constitution of India that determines how legislative powers are divided.
"Article 245 provides, inter alia, that (subject to the provisions of the Constitution).
(i) Parliament may make laws for the whole or any part of the territory of India and (ii) the legislature of a State may make laws for the whole or any part of the State.
(b) Thus, article 245 sets out the limits of the legislative powers of the Union and the States from the geographical (or territorial) angle. From the point of view of the subject matter of legislation, it is article 246 which is important. Article 246 reads as under:
"246(1) Notwithstanding anything in clauses (2) and (3), Parliament has exclusive power to make laws with respect to any of the matters enumerated in List 1 of the Seventh Schedule (in this Constitution, referred to as the "Union List"). (2) Notwithstanding anything in clause (3), Parliament, and subject to clause (1), the Legislature of any State also, shall have power to make laws with respect to any of the matters enumerated in List III in the Seventh Schedule (in this Constitution, referred to as the "Concurrent List"). (3) Subject to clauses (1) and (2), the Legislature of any State has exclusive power to make laws for such State or any part thereof with respect to any of the matters enumerated in List II in the Seventh Schedule (in this Constitution, referred to as the "State List").