Cassini growth of population between two metropolitan cities-A case study of Beijing-Tianjin region, China

The existing models of population distribution often focus on the region with a single city or even multiple centers, and lack the detailed explorations of the common and special type of urbanization areas with two centers. Taking Beijing-Tianjin region of China, which is a distinct dual-nuclei metropolitan area in the world, as an example and choosing Landsat-5 TM image in 2005, population, etc. as the data, this paper devotes to comprehending and illustrating a model of Cassini growth of population between the two metropolitan cities through the research of spatial population distribution pattern, aided with RS and GIS techniques. Main technical processes include Kriging interpolation of the population data and character simulation of the Cassini ovals. According to the calculation of a/b, a key characteristic index of Cassini growth model, the spatial structures of population distribution were given. When a/b < 1, it is a curve with two separated loops with a population density more than 3000 persons/km(2). When a/b=1, it is a lemniscate curve with a population density about 3000 persons/km(2). When 1 < a/bae2, it is a dog-bone shaped concave curve with a population density between 500-3000 persons/km(2). When a/b=ae2, it is an oblate curve with a population density about 500 persons/km(2). When a/b > ae2, there is an oval-shaped convex curve with a population density less than 500 persons/km(2). The results show that owing to the combined action and influence of the regional dual-nuclei, the population distribution of Beijing-Tianjin region is in accord with Cassini model significantly. There-fore, there is Cassini growth of population between the two metropolitan cities in Beijing-Tianjin region. In addition, the process of Cassini growth has extraordinarily instructive significance for judging the development stages of the dual-nuclei metropolitan areas.