Fighting City-Based Crime with GIS
There is widespread agreement amongst built environment professionals that if the environment is planned, designed and managed appropriately, certain types of crime can be reduced and perceptions of safety can be improved. CPTED or Crime Prevention through Environmental Design looks at the layout of an area, site or building from the persepective of crime. It then involves development of design solutions or interventions that reduce the opportunity for crime to occur. Research shows that a consistent relationship exists between crime and the structure and design of the physical environment. Added to this is the fact that the spatial and temporal distribution of people and objects is highly uneven, which is why crime is more likely to occur at particular times and places. This is where GIS can help create a clearer picture.
Harrison Grierson has recently completed a number of CPTED assessments which have successfully incorporated the use of GIS software to map the spatial extent, type and patterns of criminal offending. Earlier this year, Harrison Grierson was asked to conduct a CPTED assessment of the Manukau City central business area. The New Zealand Police (part of the Manukau City Crime Prevention and Safety Group) were able to supply extensive crime statistics for the central Manukau area. These data sets covered all crime between 2007 and 2010 and included the type of criminal activity, the date and time of the offence and the location. This information was then geo-referenced to the cadastral DCDB database so that the crimes could be mapped to the land base for further analysis.
This task was quite challenging due to the sheer volume of the data and format. It was complicated further by inconsistencies in identifying a location for a particular incident and variable or often multiple street-numbering attributed to larger commercial lots. As an example, some descriptions might include the full street address, others simply say 'Great South Road' or 'corner Great South Road and xxxx', while other incidents were identified by the name of the business outside of which the incident took place. However, after carefully analysing the Police data, Harrison Grierson was able to match 99 per cent of the crimes to specific property addresses/locations.
Several thematic maps were then created using ArcMap 9.3 to display the data. The use of GIS mapping techniques allowed the team to quickly identify the location of precise crime hotspots within the nominated study area, which were then used to help inform further physical investigation by our CPTED specialists. From this information a layering or 'sieve mapping' approach was taken whereby crime data was overlaid with cadastral boundaries, building outlines, aerial photography, movement networks, land use and active frontages to help the team understand the spatial extent and built environment cues that can increase an area's susceptibility to crime.
These results, combined with a series of site visits and consultation with key stakeholders, provided clear guidance on focusing interventions and recommendations where they were most needed. These results were presented as a series of prioritised solutions that had multiple benefits for the Manukau central area thorugh improving physical as well as perceived safety.