ABSTRACT
This chapter explores the possibility of change over time of both the size and location of areas at risk of terrorism. Thus, the spatio-temporal analysis of local risk of terrorism will lead us to investigate diffusion processes which may occur in the neighborhood of local hotspots. Areas affected by abnormally high levels of terrorist activity can be detected at various spatial scales. The size and extent of the observed hotspots are typically affected by the choice of the spatial unit—in a regular lattice model, the spatial unit corresponds to the size of a grid-cell—and the choice of a threshold above which locations are defined as areas of high terrorism intensity, also called hotspots. Terrorist groups may also decide to act far beyond their usual areas of operations and their close neighborhood. Terrorist groups may be forced to change their main target locations due to counterterrorist actions that threaten their activity.
