Geospatial analysis can be used to guide the selection of sample spacing or sampling plan design. The first step is to conduct an evaluation of the spatial correlation of existing data using one of the following EDA methods: (1) plot the empirical variogram, covariance function, or correlation function; or (2) plot the h-scatterplot. Consider whether the spatial trend should be subtracted from the data before constructing the plot. From the plot, determine the approximate correlation range of the data, which is the maximum distance over which the data are correlated. Ideally, a sampling plan defines a sample spacing less than the correlation distance between measured values of the quantity of interest. As a conservative rule of thumb, the sample spacing should be half the range of spatial correlation identified with EDA.
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