When police techniques draw inspiration from geomatics

Using KDE, it is therefore possible to generate a continuous space by smoothing discrete phenomena to determine relative values on a map. It is this methodology used by the police that Jean-Paul Kasprzyk integrated into the multidimensional SOLAP. An innovative cross. "The existing SOLAP use the vector model, which  allows the spatial aggregations only through pre-defined discrete objects (police sectors, for instance), since it is the programmer’s responsibility to define every entity separately, which preserves the pixel as a spatial unit. That’s why the maps generated in vector mode don’t take into account the space in a continuous manner." SOLAP is a recent discipline, created in Canada in 1997. At the time, researchers conceived the structure of spatial data warehouses in vector mode, because the technology is lighter than raster, and the results were already more convincing. However, to maintain user-friendliness and an interest in using SOLAP, the fluidity and therefore the speed of calculation, which depends on the amount of information on the server, remains one of the main priorities. A clear advantage of vector over raster. "We’ve only recently realised the limits of the vector format for everything concerning the study of spatially continuous phenomena, such as pollution or the climate, or, within the framework of this research, the variation in the crime rate within a town.  Furthermore, the continuous space modelled by raster offers the user more freedom when they want to include new geographic entities in their analysis. These entities must no longer be defined in advance in the data warehouse since they can be reconstructed on the fly using a set of pixels stored in the system."  

An interactive and multidimensional model

There is free access to the interface on the internet (http://nolap01.ulg.ac.be/rastercube). However, it is necessary to fill in a short registration form first. The user can then select a data set (certain types of crimes, certain months of the year, etc.) and then ask to generate a map that will aggregate them. They can also consult a series of graphs that provide information in the form of figures, such as the variation in crime over several months, etc.

Besides raster technology, a highly original aspect of the research is the multidimensional nature of the continuous analysis. "Usually", Jean-Paul Kasprzyk explains, "databases structure information in the form of tables storing lists of saved views. Here, the multidimensional character results from the fact that SOLAP functions with data hypercubes. It extracts data from the warehouse which it then arranges in several dimensions, several axes of analysis. This allows us to slice into the cube, to limit ourselves to one type of offence, for instance. We can also drill. Rather than aggregating information per month, it can be on a quarterly basis, etc. We can also play with the resolution of the map, with the number of pixels. Every operation will reveal different information, and will therefore depend on what the user is looking for." »

For now, the prototype isn’t used by the federal police. But it has only just been presented, and its future is still to be written. And even though it might not have a direct application, it opens the way for new methods, a whole new way of thinking in the approach of these GIS, which discreetly help us every day. Moreover, besides crime in Seattle and London, it can already offer other datasets. Essentially to demonstrate its adaptability, it can also show variations in temperature on the surface of the moon. Given the complete absence of offences on this satellite, the operation simply proves that the model isn't limiting to fighting crime!