is a measure of spatial autocorrelation. Like autocorrelation
, spatial autocorrelation means that adjacent observations of the same phenomenon are correlated. However, autocorrelation
is about proximity in time. Spatial autocorrelation is about proximity in (two-dimensional) space. Spatial autocorrelation is more complex than autocorrelation
because the correlation is two-dimensional and bi-directional.
Geary's C is defined as
where is the number of spatial units indexed by and ; is the variable of interest; is the mean of ; is a matrix of spatial weights; and is the sum of all .
The value of Geary's C lies between 0 and 2. 1 means no spatial autocorrelation. Smaller (larger) than 1 means positive (negative) spatial autocorrelation.
Geary's C is inversely related to Moran's I, but it is not identical. Moran's I is a measure of global spatial autocorrelation, while Geary's C is more sensitive to local spatial autocorrelation.
Geary's C is also known as Geary's Contiguity Ratio, Geary's Ratio, or the Geary Index.
This statistic was developed by Roy C. Geary.