Shape Readability

Small cartographic elements and signatures do have a lower size limit in order to stay readable and do not get mixed up. The problem is significant if the map afterwards should be generalised to a smallest scale. In order to avoid clashing elements and instead raise the readability, various graphic rules need to be considered. There are existing limits of visual perception to follow, which form the physical border for reading maps and graphics.

• Approximately, the human eye has a maximum resolution of 0.3 mm from a 50 cm distance.
• The rods and cones in our eyes set the limit to 0.0002 mm for elements perceived next to each other on the retina

Based on this and a good contrast between map elements and background, the following numeric values are needed for our eyes to perceive signatures from an approximately 30 cm distance. The values apply to stand-alone, black objects on a white background.

Minimal Dimensions

For lighter colours, the numeric values have to be modified, the elements need to be enlarged and the distance between them extended. Another interesting point of reflecting on minimal numeric values is the level of differentiation on shapes. For presenting signatures on the map, a difference in shape between two of them need to be noticeable. See the following animation for graphical explanation: