  We study the scaling of (i) numbers of workers and aggregate incomes by
occupational categories against city size, and (ii) total incomes against
numbers of workers in different occupations, across the functional metropolitan
areas of Australia and the US. The number of workers and aggregate incomes in
specific high income knowledge economy related occupations and industries show
increasing returns to scale by city size, showing that localization economies
within particular industries account for superlinear effects. However, when
total urban area incomes and/or Gross Domestic Products are regressed using a
generalised Cobb-Douglas function against the number of workers in different
occupations as labour inputs, constant returns to scale in productivity against
city size are observed. This implies that the urbanization economies at the
whole city level show linear scaling or constant returns to scale. Furthermore,
industrial and occupational organisations, not population size, largely explain
the observed productivity variable. The results show that some very specific
industries and occupations contribute to the observed overall superlinearity.
The findings suggest that it is not just size but also that it is the diversity
of specific intra-city organization of economic and social activity and
physical infrastructure that should be used to understand urban scaling
behaviors.
