An angular version of spatial correlations, with exact significance tests

Abstract

Spatial correlations are replaced by ordinary correlations by projecting the two-dimensional coordinates of a map onto a single axis making angle θ with the horizontal (east-west) axis. This calculation permits the use of exact test statistics. Moreover, the correlations can be plotted in polar coordinate form and the significance of the maximum correlation can be tested. The plot is a useful aid in assessing the reasonableness of the isotropy assumption.