Taiho Code defined the koka in the cities on both east and west of the capital, and the koka for in-kind payment of taxes on trade or taxes on fields administered directly by a ruler (jishi), such as kubunden (the farm land given to each farm in the Ritsuryo system) (or when conducting jishi trade in order to send jishi (land taxes under the Ritsuryo system to the central govenment)).
大宝律令には都の東西両市における估価をはじめ、貿易や口分田などの公田からの納税（地子）を代物で納める（あるいは、地子を中央へ送るために地子交易を行う）ときの估価などが規定されている。