border, limit, dike, frontier, boundary
埸 centers on a physical dividing line or barrier: a border, boundary, or frontier, often marked by an earthen dike or raised limit.
埸 combines 土 (earth) with 易, which likely contributes a phonetic element. The earth radical suggests a man-made earthen boundary or dike.
The left side 土 is earth, and the right side 易 looks like a sun 日 over a striped boundary marker 勿. Picture an earthen dike built under the sun to mark the border of a field.
For エキ, imagine a frontier station where travelers exchange (エキ, from 駅) their passes: the station marks the border, and エキ sounds like the first part of 駅 (えき).