It is after the end of the Great World War II that exploitation of land had been remarkably carried out at the bottoms of volcanic mountains where extensive plain spread out at their skirts. Generally speaking, there is more belated in land exploitation than other districts owing to its geographic figure, climates and soils. However hither to unavailed left as deserted place for a long time, it is considered on the other side that it has an important significance for the village life serving as the sphere of meadow land and felling of firewood and charcoals. Or it might be rather taken for a requisite area for the village life. Moreover, considering together of the fact some parts of it had been scheduled as the object of exploitation of the Shinden (newly reclaimed field), it is to be putted in mind that we should not neglect the histrico-geographical studies concerning the bottom area of volcanic mountain. From this point of view, the author here deals with the theme of exploitation at the foot of Mt. Iwaki as well as at the area of river Iwaki. In its proceeding it will be touched upon the backwardness in land exploitation at the bottom area of volcanic mountain. However, in that case, I think that it should be treated, not as a separate study on the subject of the utility of forest and lands at the skirt of the volcanic mountains, but as a systematic comprehension of these two coordinated areas with reference to the alluvial plain where exploitation of the Shinden had been energetically forwarded.
This is summimg up:
1) In the Hirosaki clan they had actively exploded the Shinden at the district centering the Tsugaru plain. In the era of Bunroku and Kan'ei (1592/1596-1624/1643) exploitation was developed according to the system of vassalage (ko-chigyô-ha dachi) in making irrigation from the middle-river of Iwaki by constructing weirs at its plain and watering from reservoirs at Tsugaru hilly country as well as from those which were built alongside of northern foot of Mt. Iwaki.
2) In the eras of Kanbun and Genbun (1611/1672-1736/1740) the Shinden exploitation was furthered at the low swamps land of the Iwaki lower stream after the “Okura-hadachi” system in setting up of reservoirs and drainages on a large scale.
3) From the era of Genbun to the era of Bunsei (1736/1740-1827/1829) the exploitation front reached Lake Juhsan.
4) In the Tsugaru district there often turned out bad harvest, “failure of crops” as they called it, due to cold weather and innundations. It brought about devastation of many fields. Therefore, special care was also payed to countermeasure against them at the exploitation of Shinden. Types of Shinden are following: Shinden exploitated by retainers (Vassalage), “Shinden constructed by the clan” (Okura-hadachi) and “Shinden operated by the clan” (Kirizoe-shinden) etc.
5) The output of Shinden crops increased from 230, 400 US bushels (45, 000 goku) in the era of Bunroku 1st (1577) to 1, 626, 280 US bushels (317, 633 goku) in the era of Keio 4th (1868). But this is only the nominal yield recorded in the village register. In the Hirosaki clan there must have been a considerably more yield which were kept out of the village register. They say that it was surmised 2, 560, 000 US bushels (500, 000 goku) in the era of Enpoh 4th (1676), 4, 710, 400 US bushels (920, 000 goku) in the era of An'ei 6th (1771), 3, 686, 400 US bushels (720, 000 goku) in the era of Ansei 1st (1854). That may be why there were many veiled fields not enumerated in the village register.
6) With the advance of the Shinden exploitation there could not be found any phenomena of devastation of old fields. We think that this was caused from the fact that there were less percentage of the registered yield than that of the unregistered in the total yield.

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The formula for delimiting theoretical tributary areas of central places has been improved by O. Tuominen, S. Godlund et al. since first studied by W.J. Reilly. Moreover, by the mutual comparison between many centrality-indices, M. Nishimura has found that the strength of two central places are directly proportional to ‘the values of retail sales - the values of retail food sales’ and inversely proportional to the square of the distances from two central places.
The objective of this paper is to find the mutual discrepances between theoretical tributary areas derived from such a method and trade areas of higher order and bus traffic areas in Okayama Prefecture as a case study, and to verify what reasons such discrepances are based on.
While Okayama and Tsuyama as higher order centres both have wide theoretical tributary areas, the higher order centres from the neighbouring prefectures such as Himeji, Fukuyama, Yonago and Kurayoshi penetrate their own tributary areas into the marginal area in fig. 2. Moreover, lower order centres such as Kurashiki, Ibara and so on have smaller theoretical tributary areas. Occasionally theoretical tributary areas of higher order centres rise again beyond ones of lower order centres on the opposite sides.
However, except for Saidaiji and Soja, lying at the distances of 11 and 20km from Okayama respectively, such a pattern can not make its appearance in the figure of trade areas (fig. 4. b. c.). For example, the trade area of Takahashi contacts directly the one of Niimi without penetrating that of Okayama; the trade area of Fukuyama does not exist in the southwestern part. In these areas few bus services radiating from Okayama and Fukuyama operate but most of them radiate from the neighbouring lower order centres.
The fact that the inhabitants in the trade area of a lower order centre depend on the centre more strongly than its own inhabitants, can not be shown also in the figure of theoretical tributary areas. For example, the inhabitants of Takahashi are supplied goods and services of higher order from the city at the rate of about 45 per cent, while the inhabitants of Matsubara village, 8km from Takahashi, are supplied goods and services of higher order at the rate of about 90 per cent (fig. 5).
It is obvious that the inhabitants of lower order centres themselves maintain a higher standard of living and the wider living areas than those of their trade areas. But, another factor is that bus service between the lower order centres and the higher order centres on which they depend is better as compared with that between the lower order centres and their tributary areas.
Therefore, it is important for delimiting theoretical tributary areas to correctly estimate “accesility to a centre” by considering not only the distance but also the frequency of bus service on every road.
Using bus service as method of delimiting tributary areas is of value, for sometimes bus traffic areas can be better superimposed on trade areas than theoretical tributary areas, though they, especially of smaller centres, are sometimes disturbed by intervening of occasional factors, and by the effects of railways; but the author thinks that it is more important to further improve the formula for the studies of tributary areas of central places.

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