Philadelphia Police Department Crime Mapping Tool

Posted by on July 6, 2008

Police open crime mapping application to public

People like to know what goes on in their neighborhoods. Most of us want to know if a new family is moving in down the block, if a store is closing or a new business opening, and, perhaps more than these, we want to know if any crimes have been committed nearby. And when it comes to something as important as crime, we want that information from a credible source.

While police departments across the country record this information, it is generally only used internally by police personnel. In recent years a relatively small number of city police departments have started making the data available to the public.

Philadelphia’s Police Department (PPD) is now one of these select police departments. In response to widespread public concerns about crime in the city, Mayor Nutter and Police Commissioner Ramsey charged the Police Department with creating a public website where city residents can map the incidence of major crimes in Philadelphia. Based on its previous work with crime analysis applications, the PPD selected Avencia, which is also working to improve the new Connect211 information and referral website, to develop the system.

The emphasis of the site is on simple, accurate display of crime occurrence across the city in a “pin map” style. All crime data is fed nightly to the site directly from Philadelphia Police Department’s databases. Up to 30 days worth of crime can be viewed simultaneously and a data download feature enables anyone to extract and download the data for more rigorous analysis.

One of the greatest challenges in creating the site was the need to display even relatively high volume of crimes at every scale. For example, theft is the most numerous of the so-called “Part 1” crimes (the more serious crimes). Viewing thefts city-wide, for a typical thirty-day period, may result in 3,000 or more data points. The map depicting this situation would simply be a mass of undifferentiated points, which is not useful to anyone.

To address this concern, the site aggregates many points concentrated in the same geography and lumps them together into a single larger point, sized proportionately to the number of points it represents. This is analogous to the size of points used to represent the population of cities in many atlases.

The website computes these new aggregations “on-the-fly” depending on how close or far one has zoomed into the map

Click here to check out the application for your neighborhood.

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