足 depicts a foot - knee on top, footprint below. As radical it marks 距 as something measured in steps. Joins 跑跟跳路, all foot-and-distance characters where movement bridges space.
巨 supplies the sound jù directly - originally a carpenter's right-angle ruler, depicting measurement itself. The same phonetic powers 拒炬苣. The combined image is feet measuring out a span - the gap between two points.
