Spot map is used for ?

Ans. is 'a' i.e., Local distribution of disease Inner and outer city variations in disease frequency are well known. These variations are best studied with the aid of "spot maps" or "shaded maps". These maps show at a glance areas of high and low frequency, the boundaries and distribution. For example, if the map shows "clustering" of cases, it may suggest a common source of infection or a common risk factor shared by all the cases. The classical example of use of spot maps was by John snow for cholera epidemic in 1854.