首楞嚴義疏注經 4.446

4.446

界之體性依假施設，雖云十方，若以位次，決定明顯。東西南北，可為準的，餘皆不定。

The substantial nature of boundaries is based on provisional designation. Although one speaks of ten directions, if examined by their positions, they are definitely distinct. East, west, south, and north can serve as standards, while the rest are all indefinite.