Like moths to a flame, people are drawn to news about crime. They want to know where, how and why it happened. But, most of all, they want to know if it could happen to them in their neighborhoods. There is no way to answer that question, but mapping crimes can help readers determine their risk.
Crime maps fall into two categories: thematic maps showing crime rates or maps plotting specific incidents. Crime-rate maps are great for comparing the relative safety of different states, cities or neighborhoods. Maps plotting specific incidents are valuable for tracking crime in small towns, a burglary ring or a serial rapist operating in a certain area.
Regardless of how you decide to map crimes, the first step is to get the incident report data from police. You need to know where the crime happened. For a crime-rate map, the 'where' needs to be a census tract, planning district, neighborhood or any other area for which you have population data. To plot individual crimes, you need an exact address or, failing that, a block number and street name.
Depicting crime rates
At The Virginian-Pilot, we publish crime-rate maps showing the previous year's property and violent crime rates for four cities in our region. Depending on the city, the maps are broken down into census tracts, police zones or city planning districts.
Mapping the crime rates, rather than the individual incidents or number of crimes, allows readers to evaluate the safety of neighborhoods throughout the city. Readers like prospective home owners often call asking for the maps; close to 15,000 people visit the online version each month.
Step-by-step
1. Get police incident data in an electronic format, including the incident number (or other unique identifier), offense, date, time, address or block number, census tract or other area for which you have population data, and anything else you can get. 2. Calculate crime rates for the census tract or designated areas, using a database manager like Access or FoxPro. (For a crime rate per 1,000 residents, divide the number of crimes in an area by the population and multiply that number by 1,000.) 3. Create the necessary census tract or area files for your mapping program. Most programs come with census tract files, and most city planning departments can provide files for other district designations the cities use. 4. Then, using the mapping program, map the crime rates you've calculated.
Plotting crimes
Plotting individual crimes can be a great tool for spotting patterns in crimes, but it is not a fair way of comparing crimes in different areas of the city. Areas that are densely populated and heavily trafficked are going to have more crimes. But if you notice a rash of rapes occurring in one geographical area, mapping will help you see any patterns. For example, in Virginia Beach, the state's largest city and popular resort area, several women living near the ocean reported being raped by a man who had broken into their homes. They gave similar descriptions of the suspect. Plotting those incidents on a map would have shown that the rapes all took place at the north end of the beach. That information alerted readers to be more cautious, to keep their windows and doors locked. Maps plotting incidents can also be useful for readers in small towns with fewer crimes. In larger cities, the sheer number of crimes makes plotting each incident impractical. But in areas with few crimes where it is possible to plot each incident, it gives readers a greater degree of specificity.
More step-by-step
1. As with the crime-rate map, get all the incident data in an electronic format. The only difference is that you do not need census tract information for this map. 2. Again, using a database manager, create a table of crimes you want to analyze. The table must include the exact address or block number and street name. 3. Make sure the mapping program includes street level information for your city. Street level information is available (at a cost) with most mapping programs. You may also be able to find a friendly person in your city planning department who can help provide that information. 4. Then, again, using your mapping program, plot the table of crimes.
Happy mapping!
Naomi Aoki can be reached by e-mail at aoki@pilotonline.com