Refers to a location that is across the street and slightly offset, not directly opposite. Often used for buildings or shops.
See also: 筋向かい
The post office is diagonally opposite this shop.
Standard spelling.
Irregular okurigana usage; less common.
Compound of 筋 (すじ, 'line' or 'street') and 向こう (むこう, 'opposite side'). The combination yields the sense of 'diagonally opposite across the street'.