Geographical analysis machine is the procedure designed to detect the clusters of rare diseases in a particular area. Circles of fixed radii are created at each point of the square grid covering the study area. Neighbouring circles are permitted to overlap to some fixed extent and many cases of the disease within each circle counted. The significance tests are then performed based on the total number of cases and on the number of individuals at the risk, both in total and in the circle in question, during the particular census year.