Map of male and female colorectal incidence and boundaries. This map shows the boundaries for male and female colorectal cancer superimposed on the map of male colorectal SMR. The blue lines are ZIP code edges. The boundaries shown as thin yellow lines indicate those ZIP codes with large changes in female colorectal cancer incidence. The boundaries shown in thick orange lines indicate the edges of ZIP codes across which there are large changes in male colorectal cancer incidence. Locations where the thick orange line surrounds the yellow line illustrate exact boundary overlap.