Spatial Auto Correlation
Definition: Spatial auto correlation is a measure of  data clustering.  Data is classified as either positive, negative or no spatial auto correlation.
  • Positive: Similar data clumps together
  • Negative: Data is evenly spaced apart (objects seem to repel each other)
  • No: No discernible pattern in the data
How to
On a polygon map for example, highly positive auto correlation exists when similarly colored polygons touch each other.  If all polygons of a certain color touch all other polygons of the same color, then there is positive spatial auto correlation.  Seeing data in this way provides information on the extent that certain types of people, for example, tend to exist close to people of similar characteristics.
Usage: Spatial auto correlation shows a type of density.  Identifying dense areas of whatever attribute is being mapped allows for potential targeting of further investigation, funding, or community change efforts.