Okatoyo - Oko

...In the broadest sense, the area includes the three cities of Kochi, Nankoku, and Tosa, as well as the surrounding towns and villages. Although it only accounts for about 10% of the prefecture's territory, the majority of the prefecture's population is concentrated there, making it the center of the prefecture in every sense. This centrality was already established in ancient times, when the provincial capital and provincial temple were located in Oko (present-day Nankoku City) on the north bank of the Kokubu River. In ancient times, most of the Kochi Plain in the narrow sense was sea, and it is clear from Ki no Tsurayuki's Tosa Nikki that several islands were formed by landforms made of Mesozoic strata.

*Some of the terminology that refers to "Oka Toyo" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…最も広義の範囲には，高知，南国，土佐の3市および周辺の町村を含み，県域の約1割しか占めないが，県人口の過半数が集中し，あらゆる意味で県の中心部となっている。この中心性はすでに古代において形成され，国府や国分寺が国分川北岸の岡豊（おこう）(現，南国市)に立地していた。古代には狭義の高知平野の大部分は海で，その中に中生層からなる地塁が島をいくつか形成していたことが，紀貫之の《土佐日記》からわかる。…

※「岡豊」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報