Pi = proportion of the landscape occupied by patch type (class) i.
Description SIDI equals 1 minus the sum, across all patch types, of the proportional abundance of each patch type squared. Note, Pi is based on total landscape area (A) excluding any internal background present.
Units None
Range 0 ≦ SIDI < 1
SIDI = 0 when the landscape contains only 1 patch (i.e., no diversity). SIDI approaches 1 as the number of different patch types (i.e., patch richness, PR) increases and the proportional distribution of area among patch types becomes more equitable.
Comments Simpson's diversity index is another popular diversity measure borrowed from community ecology. Simpson's index is less sensitive to the presence of rare types and has an interpretation that is much more intuitive than Shannon's index. Specifically, the value of Simpson's index represents the probability that any two pixels selected at random would be different patch types.