The distribution of economic power in our biggest cities is shifting as the baby-boomer generation moves into retirement.

Regions of Sydney and Melbourne, which traditionally had the highest incomes, are surrendering that position as their communities get older.

In Sydney, the affluent north shore, which takes in a swag of exclusive suburbs including Mosman, Castlecrag and Turramurra, had the weakest income growth of any part of the city between the 2011 census and 2016 census.

A decade ago the median household income in the north shore statistical district – called "North Sydney and Hornsby" by the Bureau of Statistics – was 51 per cent higher than the city-wide median. But the 2016 census, released last month, showed that premium had been slashed to 33 per cent.