Mapping dates back two millennia and beyond. Maps were functional devices used to show the location of general geographic features. Thematic maps have as their main purpose the showing of single themes. They did not appear until the late 1600's and became less commonplace by the 1860's and 1870's. In the United States, maps did not get much official treatment until 1872. Thematic maps were used for population and health. A thematic map may be either qualitative or quantitative. Qualitative maps show the locations of different kinds of things, while quantitative maps illustrate and document the amount of something. Perhaps the simplest map is the dot map, where a dot is placed on the map to show the location of a feature. Other types of maps are choropleth, dasymetric, proportional symbol, isoline, flow maps, and the area cartogram. The first period of the scientific study of crime has been called the “cartographic” or “geographic” school because the predominant form of inquiry was cartographic. One of the earliest attempts of mapping crime occurred in France in the 19th century. The “ecological school” of crime appeared around the mid-20th century. It was fundamentally concerned with the relationship of crime to urbanization, literacy, occupational differentiation, and poverty. Sociologists were among the first social scientists to map crime, especially juvenile delinquency. Sociologists have employed dot maps to chart crime and delinquency. From such maps, the reader can gain an understanding of the spatial distribution of the crime by recognizing clusters of dots. Other forms of crime mapping began to appear by 1970. Geographers were also exploring other means of showing crime activity, including connecting the residence of an offender with the place of the crime. The earliest form of thematic mapping by computer was with a program called SYMAP. Recent crime mapping can be dated to the introduction of computer graphics and computer mapping in the mid to late 1970's. In the last two decades, sociologists have examined and mapped gangs and gang activities. 14 figures, 56 references