Crime is seen and analyzed as occurring in nested sets of space and time. Discrete criminal events are enfolded in expanding layers of spatial, temporal, perceptual, and social contexts. Dimensions of crime are vectors of analysis to be followed across the layers, either inward from the widest possible context layer toward the discrete crime or outward from the discrete crime to broader contexts. Any particular layer forms a field of intersecting dimensions in which crime patterns can be analyzed. Relationships feed forward across layers over time and backward in the individual's memory of what has occurred, while relationships feed forward and backward across layers of space. Individual sites and situations can be aggregated to a broader cityscape, but the cityscape influences individual sites and situations. Crime prevention analysis is really a process that looks at the intersection of motivation and opportunity. Opportunity influences motivation and motivation influences the perception of opportunities. Crime prevention based on environmental criminology attempts to separate potential offenders from suitable targets or good opportunities by changing the attraction of activity nodes, travel paths of potential offenders and potential victims, and the character of neighborhood edges. When nodes, paths, and edges cannot be influenced at high levels of spatial and temporal aggregation, environmental criminology in conjunction with situational crime prevention looks for ways to reduce the offender's perception of good targets. 106 references, 14 notes, 2 tables, and 2 figures