ABSTRACT
Logistic regression modelling is a widely used prediction method to generate probability maps of groundwater arsenic exceeding a selected threshold concentration. In this study, we converted logistic regression modelled probability maps to a pseudo contour map which comprehensively integrated important information of several probability maps of groundwater arsenic concentrations in Gujarat state, India. The pseudo contour map of groundwater arsenic concentrations clearly and intuitively indicates high groundwater arsenic concentrations (>10 μg/L) occurring in Kachchh District and Banas Kantha District and shows groundwater arsenic concentrations in northern and central Gujarat to be slightly higher than near the western and eastern borders of the state. The cutoffs, where sensitivity equals specificity, is one of the most appropriate criteria of diagnosis of continuous probability results, better ensuring the accuracy of the generation of a pseudo contour map. However, the probability cutoff of each contour is likely different, so that the generated map is pseudo-contour rather than a contour map.
