New Zealand will gain one new North Island electorate at the 2020 election based on the troubled 2018 census.
This is pretty much what you would expect as the NI population tends to grow faster than the South Island.
ONE THIRD OF BOUNDARIES WILL NEED TO BE REDRAWN
The Representation Commission will be required to redraw the boundaries for many electorates, as about a third have populations well above or below the average size.
Actually it will be far more than one third because even electorates within the 5% tolerance will probably be affected by neighbouring seats needing to change shape.
I’d say the extra seat will be in Auckland as the areas most over quota are Papakura, Hunua and Rodney.
South Island will see some change also. Invercargill will take some land off Clutha-Southland. West Coast-Tasman will take a bit off Nelson. The two Dunedin seats need to grow so will take off Waitaki. Selwyn needs to lose some land.