Mapping crime in cities
A young researcher at the University of Liège has recently developed an interactive digital model to map and analyse information in a crime-related data warehouse according to a multidimensional approach. This type of model is known as SOLAP ("Spatial OnLine Analytical Processing"): a classic tool in geomatics, a discipline that's a cross between geography and computer science. But this type of server is usually used to generate vector maps that can only show aggregated values in a discrete, or discontinuous, space. Thanks to the use of a raster method, which develops maps with the help of pixels and not vector entities (points, lines, polygons), this new model allows the integration of a continuous space on a map that is subsequently more accurate and faithful to the user’s expectations. Faced with the onslaught of digital information, tools such as this are essential to detect and analyse what is hidden in ever-vaster databases. Moreover, this model isn’t limited to crime and could be used for other areas such as ecology, climatology and epidemiology.
At the border between geography and computer science is geomatics. A recent and still little-known discipline, which is suitably varied nonetheless. It is involved in the acquisition of spatial data, whether in the field (total station or 3D scanner), by satellite imagery or aerial photography (photogrammetry and remote sensing). The data acquired supply spatial databases (or geographic information systems) and allow an in-depth analysis of the territory. Another more familiar aspect of geomatics is now a cherished part of our daily lives: GNSS (Global Navigation Satellite System). Thanks to a constellation of satellites, GNSS is the branch at the root of all the GPS technologies found in cars, drones, aircraft, and telephones, and enables the continuous improvement of tools as famous as Google maps.
Jean-Paul Kasprzyk, a geomatician who recently defended his doctoral thesis (1), and an researcher in the University of Liège’s Geomatics Unit, has specialised in the development of tools linked to databases. "The world of databases is divided into two major branches", he summarises. "On the one hand there are transaction databases, aimed at the man in the street. These are tools that allow us to look for relatively precise information, such as a travel itinerary. And on the other hand, there is business intelligence, which takes into account various pieces of information and more complicated statistical calculations, permitting the aggregation of a multitude of data to help a restricted group of people take decisions. Business intelligence therefore develops tools that help public authorities, CEO’s, etc., to embrace the realities and large amounts of complex data, and act accordingly."
The subject of Jean-Paul Kasprzyk’s thesis relates to the latter. "Whatever the profile of the decision-makers, whether they’re private or public, as soon as they have to take digital information into account, they may be faced with such huge datasets that are impossible to interpret. To analyse them, they must be summarised and therfore aggregated." A means of aggregating these data is to use an OLAP server (OnLine Analytical Processing), a digital interface linked to a data warehouse that allows users to understand them in a user-friendly and intelligible way. An OLAP can cover all sorts of databases. However, when it integrates computer tools linked to the spatial aspect (GIS, or geographic information system), OLAP turns to SOLAP (Spatial OnLine Analytical Processing).
Organising large data warehouses
And a new SOLAP is exactly what Jean-Paul Kasprzyk was responsible for modelling. While the prototype currently seems to be able to adapt to a variety of demands, it was initially optimised for a very precise task: the management of a multidimensional data warehouse listing the crimes and offences committed in London in 2012. Its multidimensional nature refers to the possible distinction and comparison between different types of criteria, such as the type of offence (burglary, robbery, shoplifting, etc.), its location (street, neighbourhood, district, etc.), the time (month, for instance), or the profile of the perpetrators and the victims. As for choosing the capital of England, the reason is quite straightforward. "In the beginning, I was supposed to work on a Belgian database, in partnership with the federal police", the young researcher remembers. "And some of the people I was in contact with are still very enthusiastic about my work. But I was faced with structural problems and confidentiality issues. London, on the other hand, provides free access to this type of data, up to a certain level of detail. I was therefore able to easily make an inventory of a whole series of data - and there was already a huge amount - for 2012 alone. It was sufficient to start to develop the SOLAP." London isn’t the only city to provide this type of data. The police in Seattle also releases a great deal of information, which the geomatics specialist was equally able to integrate in the warehouse.
(1) Integration of spatial continuity in the multidimensional structure of a data warehouse - raster SOLAP. University of Liège, doctoral thesis in science. http://hdl.handle.net/2268/182360