Hierarchy is one of the important concepts to analyse the regional structure. The author (Ishizawa, 1984a) defined “the retail central place system” as the hierarchy of the regional urban system organized by consumers' spatial movement, and explained it using the method of dyadic factor analysis. The previous study clarified that there are two types of retail central place systems. One is organized by four levels of trade areas (trade areas at basic, town, city and regional level), and the other is organized by three levels of trade areas, lacking the trade areas at the city level in the hierarchy. The previous study made the assumption that the number of hierarchical levels in the retail central place system is not determined by the size of trade activity or the trade area at the regional level center, but is determined by the competition of the trade areas at each level. The purpose of the present paper is to verify this assumption and to examine the cause of the competition of trade areas. The Trade Areas Survey in Miyagi Prefecture executed in 1978 and in 1981 are used in this analysis. The results are summarized as follows: 1. Trade areas are divided into four levels in the hierarchy. These are trade areas of a regional level, high goods (city) level, low goods (town) level, and a basic goods (village) level, which only appears in particular cases. These are the same results as reported in 1984. 2. Motorization is diffused uniformly in Japan; this means that the consumers can visit many shopping centers easily, which promotes competition between the trade areas, especially at the high goods level. With the passing years, fewer high-goods centers are left at a high level in the hierarchy, and their former rival cities fall toward the lower level of the hierarchy. So, there remain few trade areas of high goods level consisting of numerous trade areas of low goods level. Thus the hierarchy of the trade areas is made more simple over time. 3. If competition in two regions (systems) is contained within each region, the intermediate trade center functions will become weak. The cities and towns will all fall to an equal low rank in the hierarchy with the regional center at the top. The four-level retail central place system thus becomes a three-level one (fig. 5; type A→B). If competition is strong between two regions, one regional center will become sub-ordinate to the other, but will retain its own dominance over other cities and towns. Thus, the retail central place system will again change into a four-level system (fig. 5; type D). 4. If a big store, whose head shop is in Tokyo, Osaka or Nagoya, is built in the local town, it will stop these tendencies. The town or city will retain its intermediate retail functions (fig. 5; type C).
Oita coastal plain is situated in the east-central part of Kyushu, facing Beppu Bay, the westernmost part of Seto Inland Sea. The plain mainly consists of alluvial plains of the Oita, the Ono and the other small rivers. In this paper, Holocene deposits and geomorphic development of the western part of Oita plain are discussed on the basis of drilling data, carbon-14 dates and field survey. The main results obtained in this paper are as follows: 1) Under the plain there are higher and lower terraces and valley bottoms buried with Holocene deposits. The buried lower terrace is 5-40 meters below present sea level and gradient of the surface is steeper than that of the present Oita river: 4.4 permillage toward downstream. The longitudinal profile along the Oita river indicates that it is correlated with Lower Yokcse surface which was formed during the latest glacial age. During the maximum stage cf the latest glacial age, the buried valley was formed as the paleo Oita river. The drilling data obtained in Oita plain suggested that the deepest part of the valley floor lies 39.1 meters below sea level. In the early Holocene, lower terrace and valley floor were drowned by transgression and were buried with sediments. With progress of transgression, buried higher terrace was formed as the abrasion platform. 2) The Holocene deposits are chiefly composed of sand and silt. At the midtown area of Oita city, Holocene deposits exceeds 47 meters thick, and at the reclaimed land along the coast, the thickness of the deposits are 32 meters or more. The middle mud layer yields large quantities of fossil shells e.g. Anodontia stearnsiana, Fulvia hungerfordi, Cyclina snensis etc. which indicate an inner-bay muddy and sandy bottom at that time. At the midtown area of the city, the middle mud layer occurred between 6, 250 and 3, 460 years B. P. At the locality 6 kilometers upstream from the river mouth, Crassostrea gigas is frequently found in the mud layer. The marine mud layer ranges in height from 1.5 meters to 2 meters above mean sea level. It is determined that the oystershells in upper and lower part of the layer have carbon-14 ages of 6, 600 and 7, 100 years B.P., respectively. 3) At the western part of Oita plain, Holocene transgression reaches the maximum stage in the period between 6, 250 and 6, 600 years B. P. Field evidences show that the highest sea level of this transgression is between 2 and 3.6 meters above present mean sea level. 4) In the northern part of the city, there is a remarkable change in elevation of the lower sand and gravel layer and of “Kikai-Akahoya” volcanic ash bed. This buried scarp probably corresponds to the north-thrown fault named “Nangan (South coast) Fault” by T. Shuto and M. Hitaka (1971). However, this is able to regard as the dissected valley wall during the maximum stage of the latest glacial age, since it does not continue further east, and the average slip rate of faulting is extremely high assuming that this is of fault origin.