Clusters
The concepts underlying SADIE regard a set of data as represented by regions, within
which the observed counts are either arranged effectively at random, or form local
neighbourhoods of similarly-sized counts close to one another, termed clusters.
A group of relatively high-density counts
nearby to each other is termed a patch cluster.
A similar group of relatively small,
or zero counts is termed a gap cluster.
In SADIE, spatial pattern is measured locally,
at each sampled unit, through an index of clustering.
Each unit with count greater than the overall mean is assigned a patch cluster index, which by convention is positive.
Each unit with count less than the overall mean is assigned a gap cluster index, which by convention is negative.
Each index is computed to allow for the size of the count (abundance) at each sample unit.
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