to compare, to match, to equal
坒 centers on the idea of putting things side by side to see how they measure up: comparing, matching, or making equal.
坒 combines 比 (compare) and 土 (earth), suggesting a concept of leveling or matching ground, which extends to comparing or equalizing. The exact historical development is uncertain.
Picture two piles of earth (土) placed side by side (比) so you can compare their heights and make them equal.
For ヒ, imagine comparing two heaps of earth: heap -> ヒ, and you match them until they are equal.