Fig. 4.

Nature and effects of the spatial structure of heterogeneity. When 75% of the population is favorable (a, gray squares), they form a well connected network. At 50%, both favorable and unfavorable (d, white squares) sites form isolated patches. The effect of the fraction of sites in the population that is favorable (b) or unfavorable (e) and the proportion of neighbors of the same type (c and f), a measure of clustering, on levels of disease, with (continuous lines and solid circles) or without (dashed lines and empty circles) inclusion of transmission of disease between favorable and unfavorable sites in the population.