The purpose of this study is to search for the various concepts to clarify the structure of population distribution. Although Zelinsky constructed the framework of explanation for the causes of inequality in population distribution, the reference to the concrete spatial formation were weak. So, the author wants to develop the spatial aspects further. From the retrospect of the various viewpoints and theories on the formations of region, the author draw the many key concepts as follows: Poksishefsky's cognition on the formations of settlement, cause of the dispersed settlement, the village size and its range of farming, the function and location of cities, the degree of urbanization, city size distribution, central place theory, theory of urban systems, the various location theories, theory of core and periphery, the effects of transportation system.