• The mapping of data

Data which are supposed to have a geographical correlation may be mapped: e.g. if diseases are widespread in a particular area, a map showing this correlation may be drawn. This was the case for the cholera epidemic in 1854, where John Snow showed that the highest number of death occurred near a pump in Broad Street in London.

See the page by Edward Tufte , a historian of the visual display of data (section 'Visual display')

-see Ecole des Mines

• The representation of quantities

The diagrams by Florence Nightngale (1858-59): the diagrams suggest that a higher number of soldiers die of illness caused by bad sanitary conditions than the number of those who died in battle.