There’s a couple of areas missing from that map …Bombay hills and pukekohe have significant volcanic plateaus and cones . There’s also a volcanic plateau at Waimauku but I have no idea where the cone/s are .
northland has two volcanic fields , one it a fairly straight line from glenbervie (near tutukaka) which passes through the north end of suburban Whangarei and heads west all the way to maunganui bluff at the top of baileys beach .
the second one encompasses waitangi , kerikeri , waimate , kaihohe , with scattered cones all the any up to Kaeo so probably as large as Auckland’s fie