Balanced sampling       Balanced sampling
Doubly balanced sampling
                        Doubly balanced sampling
Spatial balance measure
                        Spatial balance measure
Spatially balanced sampling
                        Spatially balanced sampling
Unequal probability sampling
                        Unequal probability sampling
local_mean_variance     Variance estimator for spatially balanced
                        samples
pips_from_vector        Inclusion probabilities proportional-to-size
sample_to_indicator     Transform a sample vector into an inclusion
                        indicator vector
