noun, used as a suffix
south of ...; ... and southward
Suffix attached to a place name or area to indicate the region south of that reference point, or including that point and extending southward.
この線路は東京以南で大きく遅れている。
This train line is heavily delayed south of Tokyo.
関東以南では梅雨入りが発表された。
The start of the rainy season was announced for the Kanto region and southward.
Compound of 以 (i, 'from; by means of') and 南 (nan, 'south'). The 以 prefix indicates a directional boundary or range.