Distribution of lower respiratory infection episodes in time and space. Each episode is mapped to the census block group in which the individual resided. Four durations are shown: 4 years (upper left), one month (upper right), one week (lower left), and a single day (lower right). Note that scale of the vertical axis is different for the upper left panel, compared to the other three. The x-axis is longitude, and the y-axis is latitude. The area with no episodes on the right border of each plot is water. Counts are shown rather than rates to correspond to the data shown in Figures 3 and 4. Variations between census tracts are principally due to the distribution of health plan members' residence locations.
Lazarus et al. BMC Public Health 2001 1:9 doi:10.1186/1471-2458-1-9