Glossary and Resources

Comparing public data sources

The City of Chicago offers public access to several sources of data on crime and violence in Chicago. These sources are outlined here along with key points about how they are distinguished from one another. Each of these data sources originate with the Chicago Police Department (CPD). 

Video Demo

This recorded demo provides an overview and detailed description of each dashboard section.


Please find definitions for terms used in the Violence Reduction Dashboard below.

The FBI distinguishes several “index crimes” for special focus due to their seriousness and frequency. Among those are several violent crimes, which are the focus of this dashboard. In this dashboard, violent crimes include: 

  1. Criminal Homicide
  2. Rape
  3. Robbery
  4. Aggravated Battery/Aggravated Assault
  5. Human Trafficking Victimizations: Commercial Sex ActsandInvoluntary Servitude 

A victimization is a unique event during which an individual becomes the victim of a crime. An individual may be victimized multiple times, and each of those events would be depicted in the data as distinct victimizations. 

The dataset is refreshed daily, but excludes the most recent complete day to allow CPD time to gather the best available information. Each time the dataset is refreshed, records can change as CPD learns more about each victimization, especially those victimizations that are most recent. The data on the Mayor's Office Violence Reduction Dashboard is updated daily with an approximately 48-hour lag. As cases are passed from the initial reporting officer to the investigating detectives, some recorded data about incidents and victimizations may change once additional information arises. Regularly updated datasets on the City's public portal may change to reflect new or corrected information. 

Fatal shooting victimizations are all homicides where the injury is caused by gunfire. 

Non-fatal shooting victimizations are all victimizations where the victim is injured by gunfire, but the injury does not result in death. 

Non-shooting homicide victimizations are all homicides caused by something other than gunfire.

The Illinois Uniform Crime Reporting (IUCR) guideline for index crimes defines criminal sexual assault as “penetration, no matter how slight, of the vagina or anus with any body part or object, or oral penetration by a sex organ of another person, without the consent of the victim.” 

The IUCR guideline for index crimes defines robbery as “the taking or attempting to take anything of value from the care, custody, or control of a person or persons by force, threat of force, violence, and/or putting the victim in fear.” This typically includes vehicular hijacking, but this dashboard has made vehicular hijacking its own distinct category. 

Vehicular hijacking victimizations include all victimizations where the victim’s motor vehicle was taken in their presence by force or by the threat of force. 

According to the Chicago Police Department’s Incident Reporting Guide, assault victimizations involve the use of force but do not involve any actual contact between the victim and offender. The dashboard only includes aggravated assault victimizations, which require deadly force to be used. An example of this would be someone being shot at but not injured. 

According to the Chicago Police Department’s Incident Reporting Guide, battery victimizations include those incidents where contact is made between the offender and the victim. The dashboard only includes aggravated battery victimizations, which require deadly force to be used. A battery victimization in this case is all incidents where the victim suffers serious injury, a deadly weapon (other than a gun) is used, or the victim is a protected employee. 

Human trafficking victimizations comprise two types: “Commercial Sex Acts” and “Involuntary Servitude.” “Commercial Sex Acts” are defined by the IUCR guideline for index crimes as “inducing a person by force, fraud, or coercion to participate in commercial sex acts, or in which the person induced to perform such act(s) has not attained 18 years of age.” “Involuntary Servitude” is defined by the IUCR as “the obtaining of a person(s) through recruitment, harboring, transportation, or provision, and subjecting persons by force, fraud, or coercion into involuntary servitude, peonage, debt bondage, or slavery (does not include commercial sex acts).” Note that the Chicago Police Department will sometimes assist federal law enforcement in human trafficking cases; data pertaining to those cases are not reported by CPD and thus not included in this dashboard. These numbers only reflect cases opened and investigated by CPD for state prosecution. 

Multi-victim shooting incidents are any shooting incident where more than one person is the victim of a gunshot injury. 

In the dashboard, we include visualizations that show the number of victimizations per 10,000 residents. By factoring in population, this creates a standardized measure—or rate—to help us compare crime and violence victimizations across geographies (e.g. community areas) that have populations of different sizes. One community area may experience a higher number of shooting victimizations than another, but they may have similar per capita victimizations.  

Population data for community areas is from the Chicago Metropolitan Agency for Planning's (CMAP) data hub. According to CMAP, this data was last updated July 2020. It is available here.

A rolling average takes the date in question and adds the victimizations together with the prior 6 days’ or 27 days' worth of victimizations. This serves to smooth the day-to-day variations and make long term trends easier to spot. We have included a 28-day rolling average that shows trends with the least day-to-day variation, a 7-day rolling average that provides a little more of the day-to-day variation in victimizations, and a daily count, which only plots that day's number of victimizations. 

ShotSpotter is a gunshot detection system designed to automatically determine the location of potential outdoor gunfire. ShotSpotter audio sensors are placed in several CPD districts throughout the city (specific districts are noted below). If at least 3 sensors detect a sound that the ShotSpotter software determines to be potential gunfire, a location is determined and the alert is sent to human ShotSpotter analysts for review. Either the alert is sent to CPD (and captured in the data provided here), or it is dismissed. Each alert can contain multiple rounds of gunfire; sometimes there are multiple alerts for what may be determined to be one incident. ShotSpotter does not exist in every CPD district, and it was not rolled out in every district at the same time. ShotSpotter was first deployed in Chicago in 2017, and sensors exist in the following districts as of the May 2021 launch of this dataset: 002, 003, 004, 005, 006, 007, 008, 009, 010, 011, 015, and 025. 

More detail on the technology and its accuracy can be found on the company’s website here. It should also be noted that ShotSpotter alerts may increase year-over-year while gun violence did not necessarily increase accordingly because of improvements in detection sensors.