Type of traditional Ainu Settlement
A kotan (Katakana: コタン) is a traditional settlement of the Ainu people.
Introduction.
Due to the scarcity of primary source materials (as the Ainu did not have a system of writing), all studies on the Ainu kotan (based on Russian, Japanese, and English works) will have different analyzations and opinions, varying largely depending on the researchers and the duration of their work. 
The word "kotan" is often erroneously translated to as a "village"; the term generally applies to all human settlements, regardless of their size. For example, in the Ainu translation of the Bible, Rome and Jerusalem are referred to as "yerusalem kotan" and "roma kotan", respectively.
Description.
Unlike other hunter gatherers, who did not settle in one place at any given time, the Ainu were highly dependent on fishing, therefore they settled by places that had good fishing (like river estuaries) and built settlements there, though depending on the season the Ainu would move to a new fishing spot. For example, if the salmon spawning grounds differed along the same stretch of river, the Ainu would migrate along with the ground, leading to kotans being built at intervals of about 5 to 7 kilometers.
Average kotans were rather small and not very populous. A kotan can be made up of around five to seven houses, though there were larger settlements of ten or more. More than 20 households generally was the result of the forced Ainu labor mobilization under the place-contract system (場所請負制) established by the Matsumae clan during the Edo period, which cannot be called a traditional-style "kotan" anymore. In 1856, Takeshirō Matsuura (an explorer in Hokkaido) reported the statistical kotan was inhabited by 10 families and 47 people in total.
A kotan generally consisted of "cise" (thatched-roof houses), "hepereset" (cages for keeping young bears usually for the "iomante" ceremony), an "ashinru" and/or "menokol" (lavatories for the males and females respectively), a "pui" (stilt warehouse for storing food), and various drying racks for wild plants, fish, and animal skins. There is usually an "nusasan" (altar) dedicated to the Inau god as well. In later years, "chashis" (Ainu fortifications) can be found around Ainu settlements. 
There was a common ground near the kotans called the "iwolo", where kotan residents were free to cut down trees, hunt, fish, and forage for wild plants and cultivate them. Adjacent kotans were invited to share the hunting grounds, conduct the "iomante" ceremony together, and most often having one chief for several kotan. Such a collection of friendly kotan are called "ekasi itokpa".
Current Ainu kotan.
There is only one Ainu "kotan" still continually inhabited to the present day, the Lake Akan kotan in Kushiro. In 1959, there were still a scattering of Ainu kotans around Lake Akan, before Mitsuko Maeda of the Maeda Ippoen Foundation (an organization that helped in conserving Lake Akan) suggested the remaining Ainu to relocate to the new land purchased by him. As the Ainu relocated to the new land free of charge, the Lake Akan kotan was created.
Use of kotan as a place name.
Each "kotan" had a unique place name, and as such, the suffix "kotan" can be found throughout Hokkaido, Sakhalin, and the Kuril islands. 
References.
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