The numbers correspond to the pictograms shown in Figure 4. Each pictogram, indicated by its number, is defined on the grid by two coordinates: one expresses its identifiability, the other its ease of interpretation. The closer a pictogram is to the top right-hand corner, the better it is; the worst are located closest to the bottom left-hand corner. A series of parallel lines with a negative slope can be drawn to separate pictograms according to their quality. The actual slope chosen determines the importance attached to identifiability. The steeper the slope, the greater the role given to identifiability.