On the Function of Two Variables of Urban Population Density

This paper is a pure theoretical attempt to explain tendencies revealed in the last decade urban researches, such as decentralization of population toward the cities suburbs, formation of polycentric cities, by a process of alteration of city traditional monocentricity, in time, due to the growth of population. It is shown that the process of alteration of monocentricity is governed by a function of two variables of urban population density. The function is developed following the observation that urban population density is dependent, in the same time, both on distance-falling with the distance from the city center- and on time-growing with the increase of population size in cities area. The city model based on the function of two variables also predicts other interesting urban phenomena, such as cities ‘’collision’’.