An analysis about the accuracy of geographic profiling in relation to the number of observations and the buffer zone

Geographic Profiling (GP) attempts to reconstruct the spreading centre of a seriesof events due to the same cause. The result of the analysis provides an approximatedlocalization of the spreading centre within an area (often represented as a red red),where the probability of finding it is higher than a given threshold (typically 95%).The analysis has as an assumption that the events will be likely to occur at verylow probability around the spreading centre, in a ring-shaped zone called the bufferzone. Obvious examples are series of crimes perpetrated by an offender (unwill-ing to perpetrate offences close to home), or the localities of spread of an invasivespecies, where the buffer zone, if present, depends on the biological features of thespecies. Our first aim was to show how the addition of new events may change thepreliminary approximate localization of the spreading centre. The analyses of thesimulated data showed that if B, the parameter used to represent the radius of thebuffer zone, varies within a range of 10% from the real value, after a low number ofevents (7–8), the method yields converging results in terms of distance between thebarycentre of the red zone and the “real” user provided spreading centre of a simu-lated data set. The convergence occurs more slowly with the increase in inaccuracyof B. These results provide further validity to the method of the GP, showing thateven an approximate choice of the B value can be sufficient for an accurate locationof the spreading centre. The results allow also to quantify how many samples areneeded in relation to the uncertainty of the chosen parameters, to obtain feasibleresults