Two application ﬁelds utilize spatial cluster analysis extensively. In crime studies, it is often referred to as hot-spot analysis. Concentrations of criminal activities or hot spots in certain areas may be caused by (1) particular activities, such as drug trading (e.g., Weisburd and Green, 1995); (2) speciﬁc land uses, such as skid row areas and bars; or (3) interaction between activities and land uses, such as thefts at bus stops and transit stations (e.g., Block and Block, 1995). Identifying hot spots is useful for police and crime prevention units to target their efforts on limited areas. Health-related research is another ﬁeld with wide usage of spatial cluster analysis. Does the disease exhibit any spatial clustering pattern? What areas experience a high or low prevalence of disease? Elevated disease rates in some areas may arise simply by chance alone or may be of no public health signiﬁcance. The pattern generally warrants study only when it is statistically signiﬁcant (Jacquez, 1998). Spatial cluster analysis is an essential and effective ﬁrst step in any exploratory investigation. If the spatial cluster patterns of a disease do exist, case-control, retrospective cohort, and other observational studies can follow up.