CBGL

Demographic data for 2000 were from the Decennial Census (2000 estimated populations for all demographic characteristics) and for 2010 were from the decennial Census (2010 estimated populations by race-ethnicity and by age) and the American Community Survey (2008-2012 five-year estimated populations for all other demographic characteristics not reported in the 2010 decennial Census) at the Census block group level [in 2010, n = 210,000 (total); area mean (interquartile range) = 36[km.sup.2] (0.49 [km.sup.2] - 9.1[km.sup.2]) (total); 1.1[km.sup.2] (0.34[km.sup.2]-1.3[km.sup.2]) (urban); 200 [km.sup.2] (32[km.sup.2]-150k[km.sup.2]) (rural)], the finest spatial scale for which detailed Census data are publicly available.

When the 1990 census is on the line in 1992, data will be available at the census block group level, a unit containing approximately 50 to 100 households.

Because household poverty status was available only at the block group level, we aggregated census block-level land cover characteristics, and the weighted distribution of each of the eight subpopulations defined by race/ethnicity and housing tenure, at the census block group level for analysis:

However, Figure 9A depicts contours based on modeling sources and receptors at the coarser ZIP code level of geographic resolution, whereas Figure 9B represents modeling at the finer census block group level. As shown in Figure 9, modeling exposure receptors at finer geographic levels of resolution (i.e., census block group rather than ZIP code) reveals localized, neighborhood-level exposure hot spots that are not apparent at coarser geographic scales--note in particular the high concentration contours that appear in central Durham under this alternative modeling approach.

In a later statewide ecologic study, we analyzed childhood cancer rates with respect to traffic density at the census block group level and, consistent with other more recent studies focused on traffic measures (Langholz et al.