The interpretation of user sketches generates research interest in the product design community since the computer interpretation of sketches may reduce the design-to-market time while giving the designer greater flexibility and control of the design process. This paper describes how cues, namely shadows and table lines used to express structural form in the drawing, may be used in a line-labelling algorithm to obtain a drawing interpretation that matches some design intent. To this extent, this paper describes canonical forms of the cues from which a combined junction and cue dictionary is created and used within a genetic algorithm framework to label the drawing. This paper also describes how such cues may be identified from the sketch.