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Sifting crime data for information you can use

For a deeper look at community-specific crime trends, the St. Petersburg Times used computer analysis to fuse neighborhood boundaries with 2009 crime statistics from the Tampa Police Department and the Hillsborough County Sheriff's Office.

Here's how we did it.

Each law enforcement agency divides areas into hundreds of "grids" for internal crime analysis and to effectively distribute its workforce. In recent months, the Times began requesting their official data formatted in a way that showed us which crimes took place in each grid.

We then obtained maps showing common community boundaries from government Web sites. For the city of Tampa, we used a map of neighborhood associations available on the city's Geographic Information Systems downloads page. For unincorporated Hillsborough, we used the most recent U.S. Census map file for the area, which is available from the Florida Geographic Data Library.

Software called ArcGIS helped merge the neighborhood and grid data. From there, we determined which grids corresponded with which neighborhoods. In many cases — especially the city of Tampa — the grids and neighborhood boundaries did not overlap exactly. Grids often straddled more than one neighborhood or area. In those instances, we combined areas with adjoining communities to give readers a feel for crime in their general region.

The numbers for each community or area were then crunched to reveal the neighborhood-level statistics.

Go to links.tampabay.com to download the data we used and to read all of the resulting stories about crime in Tampa and Hillsborough County. There, you can also find a complete list of the grids inside each Tampa neighborhood. For instance, Ballast Point in South Tampa contains police grids 189, 193 and 198. (Because of the nature of the county grid system, such a list is not available for unincorporated Hillsborough.)

Darla Cameron can be reached at (727) 893-8351 or at dcameron@sptimes.com.

Sifting crime data for information you can use 04/08/10 [Last modified: Thursday, April 8, 2010 5:20pm]

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