81. Boundary adjustments---(1) Where the boundaries of any region or
 district are altered, and any area comes within the jurisdiction of a
 different local authority,---
   (a) The plan or proposed plan that applied to the area before the
         alteration of the boundaries shall continue to apply to that
         area and shall, in so far as it applies to the area, be deemed
         to be part of the plan or proposed plan of the different local
         authority:
   (b) Any activity that may, before the alteration of the boundaries,
         have been undertaken under section 19 (changes to plans which
         will allow activities) may continue to be undertaken as if the
         alteration of the boundaries had not taken place.

   (2) Where the boundaries of any district are altered so as to include
 within that district any area not previously within the boundaries of
 any other district, no person may use that land (as defined in section
 9) unless expressly allowed by a resource consent, until a district plan
 provides otherwise.

   (3) A territorial authority shall, as soon as practicable but within 2
 years, make such changes to its district plans as it considers necessary
 to cover any area that comes within its jurisdiction, and, after the
 changes are made, this section shall cease to apply.