The horizontal axis shows the upper-bound lifetime cancer risk per million individuals exposed. The vertical axis shows individual source sectors (i.e., major, area and other, onroad mobile, nonroad mobile, and background sources). The horizontal bar for each source sector indicates the range of typical risks for different census tracts across the US. The vertical lines across each bar show different percentiles, as indicated by the key in the lower right of the chart. For example, to read the risks for area and other sources on the chart, the right-hand end of the bar shows a risk of about 70 in 1 million, denoting the 99th percentile census tract. This means that only 616 census tracts (1% of 61,641 total census tracts) have levels of area source-associated inhalation risks higher than this level. The 50th percentile line shows that half the census tracts have risks higher than 7 in 1 million. The left-hand end of the bar shows the 5th percentile of risk, about 0.7 in 1 million. That is, only five percent of all tracts have a risk from area sources that is less than 0.7 in 1 million (Ninety-five percent of all tracts have a higher area source-associated inhalation risk).