This NIJ Research Report introduces the science of crime mapping to police officers, crime analysts, and other people interested in visualizing crime data through the medium of maps. Not a technical guide to software, Mapping Crime: Principle and Practice presents a broad approach and addresses the kinds of questions crime mapping can answer and how it can answer them. More than 110 colorful maps illustrate how geographic information systems (GIS) are used to analyze crime problems. The appendix lists 50 Internet resources related to crime mapping, including Web sites displaying crime maps, GIS and analysis software, hot spot identification methods, sources of census data, and virtual reality viewers.