Layering and separation
Layering and separation is a technique illustrated, among others, by Tufte (1990) and concerns the visual differentiation of various aspects of the data. Tufte argues that
confusion and clutter are failure of the design, not attributes of information ... the point is to find design strategies that reveal detail and complexity - rather than to fault the data for an excess of complication (Tufte, 1990, p. 53).
Tufte proposes layering and separation as one of the most powerful devices for reducing noise and enriching the content in graphics, and is achieved by distinction of colour, shape, size, addition of elements that direct the attention via visual signals, or ordering data to emphasise layer differences (Ruddle et al., 2002). An example of this technique is visible in figure. It shows a city map of the centre of Florence. This picture illustrates at least 2 layers of reading: the location of historical places and the map of the streets to find a path. Colours have been used to distinguish between parks (in green), interesting places for tourists (brown), river (blue), and major streets (yellow). Shapes have been used to direct attention of tourists in historical places, and give an idea about what sort of building it is. This map can be used also by someone who is not interested in historical monuments in Florence but has to find the route to move from the train station to Piazza Signoria.