Centrography focuses on the average location or the center of gravity of the spatial distribution of a phenomenon. It uses the concepts of velocity, standard distance, and standard deviational ellipse to analyze a spatial distribution and its changes. The present analysis used data on all 612 lone-assailant rapes and rape attempts reported to the police department in San Diego, Calif., between 1971 and 1975. It found different classes of offenders to have relatively distinctive spatial distributions. Moreover, changes in the distribution of offender classes, through time, were not uniform. The pronounced numerical and geographical changes in reporting during 1975 strongly indicate that the State's revised rape law enhanced the reporting of single rapes. Centrography cannot explain the cause of crime, but it is useful in measuring the spatial expression of the wide array of social, political, and psychological forces that result in crime. Figures, tables, and 35 references. (Author abstract modified)