Nearest Neighbor Hierarchical Clusters of Deaths For Each Month. The probability for the clusters generated by nearest neighbor hierarchical clustering (NNHC) in Figure 1 is set at 0.05, the clusters displayed being first-order standard deviational ellipses. These ellipses reveal a similar pattern to the kernel density surface seen in Figure 2, namely, in the first part of the epidemic (up until August), statistically significant clusters follow a rough north-south line from the approximate area where the Emily B Souder docked, to the southeast of the French Quarter. Statistically significant ellipses also appear in the French Quarter for both August and especially September when the epidemic was at its peak (A to C in Figure 1). The inset map shows the location of the French Quarter on a yellow fever map of New Orleans from 1853, which in turn is overlaid on a current air photo of the larger city.