Sentence:  When the smaller facet-planes of Analytical Cubism were placed upon or juxtaposed with the large , dense shapes formed by the affixed materials of the collage , they had to coalesce - become `` synthesized '' - into larger planar <WSD>shapes</WSD> themselves simply in order to maintain the integrity of the picture plane . 
Meaning of the word marked with <WSD> tags:  any spatial attributes (especially as defined by outline)