length
袤 centers on the concept of length, particularly a long spatial extent or measurement.
袤 combines 衣 (clothing) with 矛 (halberd), but the historical reason for this combination in expressing 'length' is uncertain. It may have originally referred to a long garment or a measurement related to clothing.
Imagine a long robe (衣) that is so long it drags behind like the shaft of a halberd (矛). The robe's length is the key idea.
For ボウ, picture a long bow (as in bow and arrow) stretching out to its full length: bow -> ボウ, and the long robe matches that extended shape.
area; expanse; spread; span