Thematic map
Another example of early thematic mapping comes from London physician John Snow. Snow’s cholera map of 1854 is the best known example of using thematic maps for analysis of data. His method anticipates the principles of a geographic information system (GIS). He started with an accurate map of a London neighborhood which included streets and water pump locations. Onto this Snow placed a dot for each cholera death. The pattern centered around one particular pump on Broad Street. At Snow’s request, the handle of the pump was removed, and new cholera cases ceased almost at once. Further investigation of the area revealed the Broad Street pump was near a cesspit under the home of the outbreak's first cholera victim.