An electronic device has a display, one or more processors, and memory. The memory stores one or more programs configured for execution by the one or more processors. The device displays a graphical user interface having a viewport of a canvas containing a plurality of graphical information units. Each graphical information unit has (i) a respective location on the canvas, (ii) a respective size, and (iii) respective information content independent of size, displayed according to a current location of the viewport and a current scale of the viewport. The device displays the graphical information units according to relative size determination using a specific size metric, including displaying each smaller graphical information unit in front of each fully or partially overlapping larger graphical information unit, thereby displaying a visual hierarchy of the graphical information units on the canvas.