古北界

• 十(ten)ASSOCIATIVE
• 口(mouth; speech)RADICAL

Ten mouths passing word down through generations—that is something ancient.

• ⼔(person turning back; figure of person from behind)ASSOCIATIVE

Two people standing back-to-back represent North, the direction ancients faced away from.

• 田(field; land)RADICAL
• 介(in the middle; separate)PHONETIC

A boundary is the dividing line between separate fields.