  The scaling exponent of a hierarchy of cities used to be regarded as a
fractal parameter. The Pareto exponent was treated as the fractal dimension of
size distribution of cities, while the Zipf exponent was treated as the
reciprocal of the fractal dimension. However, this viewpoint is not exact. In
this paper, I will present a new interpretation of the scaling exponent of
rank-size distributions. The ideas from fractal measure relation and the
principle of dimension consistency are employed to explore the essence of
Pareto's and Zipf's scaling exponents. The Pareto exponent proved to be a ratio
of the fractal dimension of a network of cities to the average dimension of
city population. Accordingly, the Zipf exponent is the reciprocal of this
dimension ratio. On a digital map, the Pareto exponent can be defined by the
scaling relation between a map scale and the corresponding number of cities
based on this scale. The cities of the United States of America in 1900, 1940,
1960, and 1980 and Indian cities in 1981, 1991, and 2001 are utilized to
illustrate the geographical spatial meaning of Pareto's exponent. The results
suggest that the Pareto exponent of city-size distribution is not a fractal
dimension, but a ratio of the urban network dimension to the city population
dimension. This conclusion is revealing for scientists to understand Zipf's law
and fractal structure of hierarchy of cities.
