以い西せい

noun, used as a suffix

west of ...; ... and westward

Attaches to a place name or geographical reference to indicate the area to its west or extending westward from it. Often used in formal or written contexts such as maps, weather reports, and historical descriptions.

• 関かん東とう地ち方ほう以い西せいでは大おお雨あめに注ちゅう意いしてください。

  Please be careful of heavy rain in areas west of the Kanto region.

• この路ろ線せんは東とう京きょう以い西せいの駅えきには停とまりません。

  This line does not stop at stations west of Tokyo.