A geographical cluster is a localized anomaly, usually an excess of something given the distribution or variation of something else.
[1] Often it is considered as an incidence rate that is unusual in that there is more of some variable than might be expected.
Examples would include: a local excess disease rate, a crime hot spot, areas of high unemployment, accident blackspots, unusually high positive residuals from a model, high concentrations of flora or fauna, areas with high levels of creative activity,[2] physical features or events like earthquake epicenters etc... [citation needed] Identifying these extreme regions may be useful in that there could be implicit geographical associations with other variables that can be identified and would be of interest.
[citation needed] A geographical cluster is different from a high concentration as it is generally second order, involving the factoring in of the distribution of something else.
Some techniques include the Geographical Analysis Machine and Besag and Newell's cluster detection method.