Grid thematic mapping
In order to combat the problems associated with different sizes and shapes of geographical
regions, uniform grids (or quadrats) can be drawn in a GIS as a layer over the study area and
thematically shaded. Therefore, all areas used for thematic shading are of consistent dimensions
and are comparable, assisting the quick and easy identifi cation of hotspots. Bowers
et al., (2001) used this method as a component of a GIS-based database application set up
to identify vulnerable residences where target hardening was then implemented. LeBeau
(2001) also found this technique useful when mapping the volume of emergency calls and
violent offences per square mile in North Carolina.
This approach does have some limitations; the usage of grids still restricts how the
hotspots can be displayed. Spatial detail within and across each quadrat is correspondingly
lost because the crime events have to conform to one specifi c quadrat, which can then lead
to inaccurate interpretation by the map user. Additionally, many comments have been made
about the “ blocky ” appearance of this technique ( Home Offi ce, 2001 ; Chainey and
Ratcliffe, 2005 ; Eck et al. , 2005 ), which is affected by grid cell size. The solution, reducing
the size of each cell, can destroy the resolution of the thematic map by making it look
“ speckly ” and can fail to provide any useful information about where crime clusters ( Chainey
and Ratcliffe, 2005 ). Finally, grid thematic mapping suffers from the same MAUP problems
outlined above ( Bailey and Gatrell, 1995 ).
An example of a grid thematic map is shown in Figure 1d .