I am always on a lookout for good examples of maps presenting complex information in simple but very informative ways. The Washington Post map of Homicides in the District publicised on Google Maps Mania blog is a great example of a map summarising point data as coloured grid cells indicating counts of specific events in that location. Users can browse through multi-dimensional attribute data with simple drop-down selectors and the map is updated accordingly. It is a great way of demonstrating spatial distribution of events without undertaking complex spatial analysis, provided you input data is in a form of geocoded points that can be allocated to individual cells.
An alternative way of presenting the information is to use “cluster marker” approach, as in this UK version of crime stats from the National Policing Improvement Agency.
The most basic approach is to provide summary information only for administrative polygons, as in this example from the Australian Capital Territory:
UK crime statistics revisited
Mapping Crime in Canberra