An electronic device has a graphical user interface that displays a viewport of a canvas containing positioned and sized graphical information units. Smaller units are displayed in front of overlapping larger units. Relative size determination uses a specific-size-metric such as unit width. The device uses parentage determination rules to deduce a current hierarchical relationship between two units according to current sizes and positions. When there is full or partial overlap, the larger unit of each pair is deduced as the parent; otherwise there is no direct relationship. Clusters of decreasingly sized descendants result. User input adjusts the size and/or position of a selected unit while concurrently applying the adjustment proportionally to all descendants. Throughout continuous input, each adjusted and other canvas units are independently displayed with smaller in front of overlapping larger units. After the adjustment, subsequent parentage determination may deduce changed hierarchies across adjusted and other canvas units.