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Thursday, 24 December 2009

Location, Location

Continuing with the street robbery analysis in a London Borough. I am experimenting with a minimalist visualisation of the data to show how two different but connected police information systems record the location of the occurrence of the same crime type.

The top diagram shows the locations of robberies recorded on the MPS crime recording information system CRIS. Each robbery location is plotted as a point. This is then overlaid with a grid with squares measuring 250 metres by 250 metres. A spatial join of the two layers is carried out which counts the number of points (or robbery allegations) in each grid square. The grid square is coloured according to the legend with dark colours representing squares with higher number of robberies.

A robbery allegation can be made to police in a variety of ways. One of which is by telephoning 999 if the robbery has recently occurred. Police treat such incidents as emergencies and respond immediately. These incidents are recorded on the MPS Computer Aided Dispatch (CAD) system. Not all calls result in an allegation of robbery being recorded on the CRIS system. The middle diagram shows police emergency robbery calls plotted in the same way as the CRIS allegations.

The bottom diagram is showing the two diagrams above merged with the layers on top of one another to show the similarity and differences in the locations.

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