The VARIOGRAM Procedure
Autocorrelation Statistics
Spatial autocorrelation measures offer you additional insight into the interdependence of spatial data. These measures quantify the correlation of an SRF 
with itself at different locations, and they can be very useful whether you have information at exact locations (point-referenced
data) or measurements that characterize an area type such as counties, census tracts, zip codes, and so on (areal data).
As in the semivariogram computation, a key issue for the autocorrelation statistics is that you work with a set 
of measurements, 
, that are free of nonrandom surface trends and have a constant mean.