Figure 3. Spatial-temporal distribution of incidence of smallpox during outbreak, by district, Liverpool, 1902–1903 (7). *Incidence of smallpox per district (per 100,000) calculated as number of cases per district ÷ by district population x 100,000. New cases per district were counted from their locations given on the 4 maps in the original report for each of the periods above. District populations were tabulated separately (7).