Leicester space technology and those maps of crime statistics

Posted by mjs76 at Feb 03, 2011 04:48 PM |
Press coverage of the ‘crime maps’ of England and Wales this week has tended to concentrate on the ‘crime’ angle (and the crashing servers angle) rather than maps themselves, which were produced with help from the University of Leicester.
Leicester space technology and those maps of crime statistics

example of a Voronoi diagram (image: Wikipedia)

Rock Kitchen Harris, the agency which produced the maps for the Home Office and the National Policing Improvement Agency (NPIA) had a daunting logistical challenge. There are 476,000 ‘snap points’ across the maps, each giving crime figures for that particular locale. It was very important that snap points should be in the middle of roads and not on top of any particular building. Another specification was that each snap point must cover no fewer than twelve homes (however spread out along the road the houses might be).

What RKH had to produce was a Voronoi diagram (named after Ukrainian mathematician Georgy Voronoy) which is a way of mapping an area into contigious polygons with no overlaps and no spaces. Each polygon in a Voronoi diagram contains one of a designated set of points (in this case, all the crime figure ‘snap points’) and – this is the important bit - all points within that polygon are closer to that designated point than to any other designated point.

Dividing England and Wales up into 476,000 irregular, interlocking polygons was just too much for RKH’s computers but fortunately they already knew the folks at G-STEP, our Space Technology Exchange Partnership, who had the expertise and the software to work it all out.

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