Figure 6.30 Time lag maps for infectious diseases in Iceland, 1900–90. Average time in months from commencement of epidemics to reach medical districts in different parts of Iceland. On each map, medical districts reached for the first time are shown as solid circles. Districts appearing on earlier maps appear as open circles on later maps. Circle sizes are proportional to 1990 medical district populations. (A) Measles. (B) Rubella. (C) Pertussis. (D) Average across all three diseases and influenza.