We studied how graph design principles can predict specific reasoning mechanisms that occur when misinterpreting box plots, and, more specifically, the misinterpretation of the area as a representation of frequency or proportion of observa tions, instead of density. In previous studies this misinterpretation has been shown to be heuristic in nature and is elicited by the fact that box plots do not use space in a natural way. Graph design principles provide a theoretical framework for assuming that the orientation of a box plot could influence its interpretation. By analyzing reaction times and accuracy rates for different item types, we explored whether there indeed is an influence of the orientation of a box plot on the way it is interpreted. Results indicate that the misinterpretation manifests itself in both orientations to the same extent, suggesting that the orientation of a box plot does not influence the reasoning mechanisms it provokes.