Radical 广 (broad, shelter) over the phonetic 郭 - and 郭 itself meant 'outer city wall.' So 廓 = the wide outer enclosure, hence both 'outline/contour' (轮廓) and 'vast/wide-open' (寥廓 'boundless,' 廓清 'to sweep clean').
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Bound form - almost never stands alone. Most common compound: 轮廓 (contour/outline).
Upper-left shelter radical - a roof leaning out from a wall. Indexes 廓 in the building family alongside 庙、府、庭、库. Here it frames the meaning 'outline, contour, expanse' as the outer wall of a settlement - what you draw around the inside.
Inside, 郭 supplies the sound guō to kuò and pulls double duty semantically: 郭 itself means 'outer city wall,' so 廓 directly inherits the 'enclosing perimeter, broad outline' core. Same phonetic family as 椁 (outer coffin).
