Publications of Marie Trotta
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See detailImpact de l’anisotropie du milieu dans les études de profilage géographique
Trotta, Marie ULg; Deprez, Cécile; Donnay, Jean-Paul ULg

in SAGEO 2014, Grenoble 24-27 November 2014 (in press)

This communication aims at assessing the bias introduced by the use of the Euclidean distance in the context of geographic profiling analyzes. It proceeds by a comparison of road and Euclidean distances ... [more ▼]

This communication aims at assessing the bias introduced by the use of the Euclidean distance in the context of geographic profiling analyzes. It proceeds by a comparison of road and Euclidean distances of about 1 000 pairs of origin-destination (crime sites – criminal’s anchor point) from the database of the Belgian Federal Police. Comparisons are differentiated by the density of road network (rural and urban areas) and the statistical parameters of the resulting distributions are exploited in the application of the most common geographic profiling model called the distance decay model. [less ▲]

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See detailModelling serial offenders’ spatial behaviours: new assumptions for geographic profiling
Trotta, Marie ULg

Doctoral thesis (2014)

The geographic profiling is amethodology of investigation which uses the crime sites of a criminal series in order to delineate prior areas for searching the offender. Its implementation is currently ... [more ▼]

The geographic profiling is amethodology of investigation which uses the crime sites of a criminal series in order to delineate prior areas for searching the offender. Its implementation is currently limited by too simplistic assumptions that are difficult to assess during an investigation or even not corroborated at an individual level of observation. This thesis studies the predictive capacities of geographic profiling in the context of Belgium, a dense country where the road network is not suitable for classical algorithmimplemented with Euclidean or Manhattan distances. More precisely, the thesis has for first objective to integrate space anisotropy with two improvements: (1) the integration of the road network in the journey-to-crime and (2) the integration of the structure of opportunities for series of sexual offences. Beyond this objective, the thesis questions a hypothesis underlying this type of research methodology: the kind of spatial relationship between the offender’s residence and the crime sites. An alternative to the distance decay effect is developed, minimising the variance in travelled distances between the offender anchor point and the initial contact sites of the offences (MOV hypothesis). The sensitivity of this methodology is measured and its effectiveness is compared to the one of the distance decay effect. A major result of the thesis is that the share of behaviours than can be modelled by this new hypothesis is similar to the one of the distance decay effect. However, a large number of series did not meet the required conditions to implement an efficientmethodology given the multiplicity of offender’s residences or the scarcity of sites composing the series; those applicability criteria are analysed in this work. Nevertheless, theMOV hypothesis is particularly valuable for long series of offences. Then, the thesis analyses the impact of the geometry of crime series locations on the effectiveness of the chosen spatial assumption (distance decay effect orMOV) with graph theory. It highlights the superiority of the MOV hypothesis for offenders travelling in some preferred direction. The analysis also shows that both hypotheses are not mutually exclusive but can be combined to build offender geographic profiles. Finally, this thesis focuses on the modelling of neutral areas in terms of criminal attractiveness on the Belgian territory. The work presents the originality of analysing data on a whole country, integrating both urban and non-urban areas. The objective of the modelling is the integration of the opportunity structure of sexual offences in the geographic profile and the estimation of the perturbing effect of a differentiated attractiveness. In order to assess this perturbation, we propose a two-steps process. Firstly, a regression model combining factors fromthe crime pattern and social disorganisation theories models the spatial distribution of crimes. The regression model identifies a centre-periphery relationship in the spatial distribution of crime locations. Still, the model underestimates the number of positive sectors, omitting some attractors. Then, the impact of attractive location (i.e. presenting the favourable factors for crime concentration)is evaluated for the series of sexual offences. In fine, the two spatial hypotheses do not seem affected by the attractors identified by the modelling except when the contact sites are clustered in attractive areas. In addition, the share of serial offenders committing their offences in the most attractive locations is smaller than that of single offenders. This observation strengthens the need for working on spatial distribution models instead of calibrated functions with solved cases. [less ▲]

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See detailCrime Hotspots In Belgium: Spatial He terogeneity In The Multivariate Regression Model?
Trotta, Marie ULg

Conference (2014, June)

Place attractiveness is an important property to consider when modelling the spatial behaviour of a serial offender. Small spatial units are privileged in the recent literature to study the crime ... [more ▼]

Place attractiveness is an important property to consider when modelling the spatial behaviour of a serial offender. Small spatial units are privileged in the recent literature to study the crime concentration-urban backcloth relationship, with the drawback of focusing on a single city. However, the urban backcloth is also shaped by the inter-cities and city-hinterland relationships. Our objective is to model the concentration of sexual offences for entire Belgium, at the very precise scale of the statistical sector in order to take into account the role of the urban hierarchy. Methods: We analyse the ViCLAS data for Belgium between 2004 and 2011. Specifically, we study the relationship between the concentration of initial contact scenes and socio-economic characteristics and facilities of the statistical sector, using two spatial models. First, we computed a spatial lag zero-inflated model (ZINB) in order to evaluate the global predictive capacities of the model. Then, a Poisson geographically-weighted regression (GWR) was run to study the spatial heterogeneity for each of the explanatory variables. Results: The zero-inflated negative binomial model with spatial lag recovers the neighbourhood environmental quality, the concentration of economic and cultural activities, and drinking places as major significant factors (Mc Fadden’s pseudo-r² of 0.2). The Poisson geographically-weighted regression underestimates the crime concentrations but highlights the spatial heterogeneity [less ▲]

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See detailSelection of a spatial hypothesis in geographic profiling using graph theory
Trotta, Marie ULg

Poster (2013, May)

Geographic profiling is based on the spatial hypothesis of a distance decay effect around the offender’s anchor point and can be very useful for delineating prior search areas for individual ... [more ▼]

Geographic profiling is based on the spatial hypothesis of a distance decay effect around the offender’s anchor point and can be very useful for delineating prior search areas for individual investigations such as DNA testing. However, this spatial hypothesis fails to model a significant part of Belgian serial sexual offenders. In previous study, a complementary hypothesis, the minimisation of the variance (MOV) for the distances between the offender’s anchor point and the crime site, exploiting recent literature observation, is proposed to model unexplained behaviours. A systematic comparison of the distance decay and the MOV hypotheses show that their overall capacities to provide an effective geoprofile are similar, but their performances may differ, depending on the geometric pattern of crimes. Here, we use graph theory to describe the favourable patterns for the MOV, in order to select which spatial hypothesis is best suited for a new investigation. While star graphs represent patterns for which both hypotheses could be validated, wheels with preferred directions are only explained by the MOV hypothesis. Real patterns on the road network are a-posteriori evaluated thanks to the generation of the shortest path between the best solution of the MOV and all the crime locations thanks to the Dijkstra algorithm. [less ▲]

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See detailMéthodologie de recherche en cartographie criminelle
Donnay, Jean-Paul ULg; Trotta, Marie ULg; Kasprzyk, Jean-Paul ULg

Scientific conference (2013, April 26)

Presentation of the original research methods conducted by the Geomatics unit of the University of Liege, on environmental criminology, geographic profiling, and business intelligence in crime mapping.

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See detailOperationality of geographic profiling through a hypothetico-deductive method. A review of constraints and factors.
Trotta, Marie ULg; Lemaître, André ULg; Donnay, Jean-Paul ULg

in Bulletin de la Société Géographique de Liège (2013), 60

This paper is dedicated to the identification of the constraints and factors enabling the computation of an effective geographic profile, with the specificity of focusing only on the elements that could ... [more ▼]

This paper is dedicated to the identification of the constraints and factors enabling the computation of an effective geographic profile, with the specificity of focusing only on the elements that could be available during an investigation. It aimed at filling the gap between the inductive demarche of environmental criminology and the deductive, operational procedure followed by geographic profilers. It reviews successively the relationship between the premeditation, the seriousness of the facts, the nature of the offences and the spatio-temporal pattern of the crimes with the criteria required to build effective likelihood surfaces in geographic profiling. A decision tree is provided as a tool for evaluating the risks of an ineffective geographic profile with regard to the non-respect of the different conditions. [less ▲]

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See detailReconstitution of the Journeys to Crime and Location of Their Origin in the Context of a Crime Series. A Raster Solution for a Real Case Study
Kasprzyk, Jean-Paul ULg; Trotta, Marie ULg; Donnay, Jean-Paul ULg et al

in Leitner, Michael (Ed.) Crime Modeling and Mapping Using Geospatial Technologies (2012)

In the region of Charleroi (Belgium), a series of criminal acts were committed by the same group, using the same vehicle. The events were located in space and time. The car used during these criminal ... [more ▼]

In the region of Charleroi (Belgium), a series of criminal acts were committed by the same group, using the same vehicle. The events were located in space and time. The car used during these criminal activities was stolen (first event) and was later retrieved (last event) after a period of 4 days of offences. Police recorded a crucial clue: the total mileage covered by the vehicle between the first and the last event was estimated with an admissible approximation. Thanks to this information, we were able to choose the most probable journey-to-crime among several scenarios. These depended on the combination of cost surfaces built with distance propagation algorithms starting from each criminal event in raster mode. The distance propagations were limited to the road network and the combinations of the cost surfaces had to respect the chronology of the facts. The most plausible scenario suggested that the criminals hided the car into a withdrawal site between their activities. In order to improve the precision of the location of this withdrawal site, we used a multi-criteria analysis taking account of the journey of the vehicle and other environment variables. At the end of these treatments, the small stretch of road that we isolated actually included the withdrawal site, as confirmed by the police later [less ▲]

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See detailNew Hypotheses on serial offender's spatial behaviour
Trotta, Marie ULg

in Pundt, Hardy; Bernard, Lars (Eds.) Proceedings 1st AGILE PhD School (2012, March)

Geographic profiling is a methodology used to delineate a prior search area for a serial offender. Two new hypotheses integrating recent researches on offender’s behaviour are proposed to broaden the ... [more ▼]

Geographic profiling is a methodology used to delineate a prior search area for a serial offender. Two new hypotheses integrating recent researches on offender’s behaviour are proposed to broaden the applicability of the techniques of geographic profiling to commuters and irregular patterns of crimes. The journeysto- crime variance and place attractiveness will be successively integrated in GP methods. In order to evaluate the variance of the journeys-to-crime on real road network, a method based on least square adjustment in raster mode is developed. A real case of serial rapes illustrates the effectiveness of those assumptions for a non-uniform pattern of crimes. [less ▲]

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See detailBehind Rossmo's assumptions: further hypotheses to make geographic profiling more operational
Trotta, Marie ULg

Conference (2011, November 03)

Funded by the Belgian National research fund (FRS-FNRS), I am currently collaborating with several services of the federal police of Belgium (strategic, operational and behavioural analysts) to develop ... [more ▼]

Funded by the Belgian National research fund (FRS-FNRS), I am currently collaborating with several services of the federal police of Belgium (strategic, operational and behavioural analysts) to develop operational techniques to implement geographic profiling – including temporal aspects of crime scene – on the Belgian territory. Belgium is characterized by a small and highly populated territory with a complex road network; which require more concerns about its geographical features than the regular grids of American cities. <br /> <br />From an operational perspective, few studies have focused on the conditions favouring the application of GP. Rossmo defined five criteria for effective likelihood surface, but these criteria are often difficult to verify with the data gathered during the investigations. This presentation proposes to study the relationships between those applicability hypotheses, crime types, and spatio-temporal aspects of the crime in order to better predict the surface effectiveness. <br /> <br />Then, we discuss the difficulty to meet those assumptions for serial rapes in Belgium. Non-uniform pattern and multiple residences for offenders are some of the factors hampering those assumptions. <br /> <br />An unsolved case of rapes submitted by the police illustrates how a GP reasoning is still possible when Rossmo’s criteria are not met. The objective was to delineate a priority area around crime locations for DNA testing as the offender was assumed to be local. The series presents a pattern focusing on two different city centers. For this reason, the likelihood surface was generated under a different assumption than the classical distance decay. Indeed, our analysis of the crimes pattern in relation to the road network points out a new hypothesis for the offender’s spatial behaviour: spatial consistency in travelled distances to commit the crimes instead of a distance decay function. <br /> <br />This hypothesis was supported by an analysis of the ‘neutrality’ of the series crime locations. Brantingham distinguished crime generators/attractors from neutral places as a function of the attractiveness of place. According to him, distance decay functions can only be applied to neutral places. In our series, it appears that only one location was located in rural area, in a very unattractive place for rapes. By contrast, the others were located in the city centers or near night clubs. We concluded that there was a high probability for the offender to come from this village. Subsequent DNA analyses of the residents of that village confirmed our hypothesis. [less ▲]

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See detailDetermining the Geographical Origin of a Serial Offender Considering the Temporal Uncertainty of the Recorded Crime Data
Trotta, Marie ULg; Bidaine, Benoît ULg; Donnay, Jean-Paul ULg

in GEOProcessing 2011 : The Third International Conference on Advanced Geographic Information Systems, Applications, and Services (2011, February)

Since the days the investigating officers used ”pin maps” to locate and to think about crime events, crime mapping has become widespread thanks to spatial analysis mainly supplied by GIS-like software. In ... [more ▼]

Since the days the investigating officers used ”pin maps” to locate and to think about crime events, crime mapping has become widespread thanks to spatial analysis mainly supplied by GIS-like software. In particular these methods suit well to geographic profiling devoted to crime series characterised by a single offender and hence limited space and time variability. Although spatial techniques are now regularly performed to delineate an offender’s area of residence, the temporal dimension is underemployed due to the wider uncertainty of time records. This paper proposes a methodology based on a least-squares adjustment in order to cope with this temporal issue for determining the most probable offender’s residence. Moreover, a chi-square test is described to check the significance of the solutions suggested by the method. The process is carried out on the real road network which has been discretised (rasterised) for computing convenience. Three simulations show the validity of the reasoning. Finally the main time and speed assumptions introduced in the model are discussed paving the way for further research. [less ▲]

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See detailSerial offenders' spatial behaviour: revisiting the marauder/commuter dichotomy
Trotta, Marie ULg

Conference (2010, September 10)

Geographic profiling is a methodology that uses the location of a series of crimes attributed to the same offender in order to determine the residence of this latter. This recent discipline links the ... [more ▼]

Geographic profiling is a methodology that uses the location of a series of crimes attributed to the same offender in order to determine the residence of this latter. This recent discipline links the theories of environmental criminology, such as the routine activity theory, with the techniques of spatial analysis offered by the Geographic Information Systems such as centrographic statistics and distance decay functions. The literature differentiates two categories of serial offenders according to their mobility: the marauder committing his crimes in the nearby area of his home and the commuter travelling outside his daily activities area. Until now, geographic profiling methodologies have proven to be effective only for the marauder behaviours. Before applying these spatial techniques, it is therefore essential to know what kind of offenders we are facing. However, few studies have tried to determine how these two behaviours could be identified on the basis of crime scene information and suspect’s characteristics. Moreover, spatiotemporal aspects have very often been underexploited. After an introduction to geographic profiling, we present the existing typologies of offender spatial behaviours, among which the commuter/ marauder dichotomy. We set out the crucial information identified in the literature aiming at their differentiation and their implication on the method used to reduce the search area. We draw a conclusion that some spatial inconsistencies persist, requiring to revisit the typologies according to multiple spatiotemporal patterns. Particularly we demonstrate how these typologies can be enhanced by taking into account the relation between the moment of the crime and the location of the crime site. Finally, we show that these new patterns can improve the analysis of commuters thanks to techniques based on spatiotemporal constraints. [less ▲]

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See detailReconstitution of the journeys to crime and location of their origin in the context of a crime series. A solution for a real case study.
Trotta, Marie ULg; Kasprzyk, Jean-Paul ULg; Donnay, Jean-Paul ULg

Conference (2010, April 15)

Dynamic studies in crime analysis usually use distance-decay models applied on isotropic surfaces. If the distance actually traveled within the context of a crime series can be estimated, another approach ... [more ▼]

Dynamic studies in crime analysis usually use distance-decay models applied on isotropic surfaces. If the distance actually traveled within the context of a crime series can be estimated, another approach, independent of the widely discussed form of the distance decay, can be suggested. Besides, there is a need for studies on anisotropic space, especially in European cities, given their complex road network. Therefore, this study takes this aspect into account. We use data of a real case provided by the Belgian Police Department. Five criminal events have been committed in a short period of time by individuals using the same stolen car before abandoning it. The milometer allowed the Police to estimate the mileage covered by the criminals. The purpose of the analysis is to map out all the possible journeys to crime in order to find the offender's hideout. First, we generate cost surfaces propagated from the locations of the criminal events over the dense road network in a high-resolution raster file. This provides a distance value for all pixels of the potential paths to each crime. Then these distances are cumulated for all criminal events and the sum is confronted to the recorded mileage. This gives a restricted list of road sections from which all event locations can be reached under the constraint of the mileage covered. These results are then refined through a multi-criteria analysis using exogenous data, such as land covers. The small area finally identified contains indeed the hideout as confirmed by the Police Department. [less ▲]

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See detailÉvolution(1979-2008)des services d'hospitalisation en Belgique. Quel(s) liens avec la hiérarchie urbaine?
Trotta, Marie ULg

Conference (2010, February 24)

L'organisation de l'offre hospitalière ainsi que sa planification se voient aujourd'hui bouleversées par les logiques de marché ou d'efficience progressivement introduites dans le système hospitalier en ... [more ▼]

L'organisation de l'offre hospitalière ainsi que sa planification se voient aujourd'hui bouleversées par les logiques de marché ou d'efficience progressivement introduites dans le système hospitalier en Belgique comme dans les pays voisins. Ce bouleversement n’est pas sans impact sur l’organisation spatiale des services de soins. Toutefois, si certains auteurs y voient un renforcement de la relation à la hiérarchie urbaine, d’autres soutiennent l’hypothèse de l’émergence d’un tout autre modèle organisationnel : le réseau. L’objectif de cette recherche était de comparer l'organisation spatiale des services d’hospitalisation juste avant l’introduction d’un moratoire stoppant la croissance hospitalière (année 1979) avec la situation actuelle (année 2008) au travers de leur relation à la hiérarchie urbaine sur le territoire belge afin de soutenir l’une ou l’autre hypothèse. Si un renforcement de la relation n’apparaît que très légèrement, on a surtout pu démontrer un comportement différencié selon le type de services analysés et leur place dans la pyramide des soins. Promoteur du Mémoire : Bernadette Mérenne-Schoumaker. [less ▲]

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See detailÉvolution (1979-2008) des services d'hospitalisation en Belgique. Quels liens avec la hiérarchie urbaine ?
Trotta, Marie ULg

in Bulletin de la Société Géographique de Liège (2009), 53

This research compares the spatial pattern of services provided in hospitals just before the introduction of the moratorium stopping the growth of the hospital sector (1979) with the current situation ... [more ▼]

This research compares the spatial pattern of services provided in hospitals just before the introduction of the moratorium stopping the growth of the hospital sector (1979) with the current situation (2008) by their relationship to urban hierarchy. The method used to analyze this relationship is the application of the statistic coefficient ϒ. This work shows that this relationship is significant for the two studied periods. However, the presence of a nearby faculty of medicine appears to interfere significantly on this relationship. The study also highlights a slight tendency to the strengthening of the aforementioned relationship. Besides, it demonstrates the existence of different spatial behaviours depending on the type of service. [less ▲]

Detailed reference viewed: 163 (54 ULg)