Criminologists have expanded their use of maps as the costs of mapping have decreased dramatically. Using two cases of drug dealing, this chapter examines the way in which theory influences map interpretation. The first study is a hypothetical case using fictitious data; the second, an actual case using real data. When the explicit theoretical contents of maps was low, it was difficult to interpret the data. As the theoretical content of maps increased, their utility increased. The study also showed that theory enhances the utility of computer algorithms designed to find point clusters on maps. The same distribution of points on a map may lead to a number of different potential explanations. More often than not, it is difficult to make sense of the mass of data that computer maps provide without informing analyses with theories about the distribution of crime events. The article discusses the implications for crime control and prevention practitioners and researchers. Figures, notes, references