I was listening to a BBC Radio 4 programme on language and was interested to hear about the ranges of accents across a country. The theory was that America was settled without the benefit(?) of mass communication, so the people in the deep South lived in isolation from those in the North and so dialects developed independently. Radio arrived much later and only then did most ordinary people to hear other accents. In Australia and New Zealand there was a much shorter gap between the different cities becoming more populated and the arrival of mass communication.

What I was wondering is - what are the distinctive differences between
Perth and Melbourne
and also
the North and the South Island of New Zealand?

What about Cananda - what are the differences between, say Vancouver and Toronto?