  Fractal structure of a system suggests the optimal way in which parts
arranged or put together to form a whole. The ideas from fractals have a
potential application to the researches on urban sustainable development. To
characterize fractal cities, we need the measure of fractional dimension.
However, if the fractal organization is concealed in the complex spatial
distributions of geographical phenomena, the common methods of evaluating
fractal parameter will be disabled. In this article, a new model is proposed to
describe urban density and estimate fractal dimension of urban form. If urban
density takes on quasi-fractal pattern or the self-similar pattern is hidden in
the negative exponential distribution, the generalized gamma function may be
employed to model the urban landscape and estimate its latent fractal
dimension. As a case study, the method is applied to the city of Hangzhou,
China. The results show that urban form evolves from simple to complex
structure with time.
