The main feature of the central place theory is to study the town as a system based on service function. The basic argument comes from the works published by French L. Lalanne in 1863 and German R. Gradmann in 19 16 respectively, that is, towns were formed in a certain number of production sites. Cities and towns are the projection of human social and economic activities in space and the core of the region. Cities and towns should be built in the center of rural areas and play the role of surrounding rural centers. From the center, it relies on collecting and transporting local products and providing needed goods and services to the surrounding rural population. Based on this basic argument, through the investigation of towns in southern Germany, Christalle assumes that the conditions of the central area are as follows: ① On the homogeneous plain with uniform distribution of soil fertility and resources, the population distribution is uniform, and the income is consistent with the demand for goods and consumption patterns. ② The transportation system is unified, the traffic conditions of towns of the same scale are the same, and the transportation cost is directly proportional to the distance. (3) Producers strive to obtain as large a market area as possible, and consumers strive to obtain goods and services from the nearest place. (4) The actual cost for consumers to buy goods and obtain services in the nearest center is equal to the sales price plus transportation expenses. Christalle believes that the nearest and most convenient place to provide goods and services should be located in the center of the circular market area. And if the circular market areas are tangent to each other, there will be consumers who cannot supply. Only when the circles overlap can we meet the needs of all consumers. According to the assumption that consumers prefer the nearest supply point and the overlapping area is equally divided by the adjacent markets, the central area is transformed into a hexagonal system.

The size of towns around the world is inversely proportional to the number. The smallest towns have the largest number and the largest towns have the least number. The higher the level of cities and towns, the less the number, thus forming an orderly hierarchy. Christalle analyzed the conditions for the formation of the central place system and called the area served by the central place as the supplementary area. He believes that the grade of the central place depends on the size of the adjacent supplementary areas, and the grade system is restricted by the following three principles (Figure 2): ① the principle of market optimization. With the development of social division of labor and market economy, regional centers often become concentrated places for commercial markets and service institutions. Under the most convenient conditions for providing goods and services, the hierarchical structure of the central place should be composed of three low-level areas 1 high-level area unit, in which the high-level central place serves two adjacent low-level central places, and the service scope is extended to three areas. In the central arrangement system (Figure 3), 3 is a constant, that is, K=3, the regional series is 1, 3,9,27,8 1, …, and the central point series is1,2,6,18,54. ② The principle of traffic optimization. The intersection of traffic lines often produces towns. On the premise of the most economical and reasonable transportation network, the structure of urban network should be: a sub-center is formed at the midpoint of the transportation line between two central places at the same level, and many small towns may be located on the transportation line between larger cities. In the central place arrangement system, the constant K=4, that is, a higher-level central place serves three adjacent lower-level central places and has its nearest service area with a same-level central place. The regional series is 1, 4, 16, 64, …, and the central point series is 1, 3, 12, 48, … ③ the principle of administrative optimization. In order to carry out administrative functions, a country or region is often divided into administrative regions at all levels and set up various administrative centers, which has a great influence on the formation of urban system. The central place system, which is most convenient for administrative management, should be composed of grass-roots units with equal distance and evenly distributed throughout the country (region). Administrative districts at all levels are managed by administrative centers located in the center of a hexagon, with grass-roots administrative centers located at all corners of the hexagon, and the smallest administrative unit consists of seven grass-roots units. However, in order to effectively perform administrative functions, the service areas of each center are clearly defined and do not complement each other. This arrangement of central locations is called K=7 system, regional series 1, 7,49,343, …, central point series 1, 6,42,294, …. Synthesizing the three principles, Christalle draws a conclusion about the number of towns at all levels in a country, and on the basis of analyzing the distance and scope of population and services in towns in southern Germany, he divides the towns in this area into seven groups, namely, market villages, town centers, local centers, regional cities, small state capitals, provincial capitals and regional capitals.