Home Map Help FAQ Trouble

Frequently Asked Questions and Answers

Q. Why can't I see the specific addresses of crimes?
A. Addresses shown at the block level only, and specific locations are not identified. This is done to protect the privacy of crime victims. Although general crime locations can be seen on a map, these placements cannot be used to derive the specific house or location where a crime may have occurred.

Q. Does a mapped incident mean an arrest was made?
A. Mapped incidents are based upon reported crime, not arrests. However, if an arrest was made, it will be noted in the crime table." In some situations, especially involving narcotics or other vice cases, the arrests indicated in the table may actually represent multiple arrested offenders, as one case report is used for all arrests related to that particular incident.

Q. Why can I only search for 14 days at a time during a 90-day period?
A. The date range has been limited to reduce the load placed on the web server and make the map easier to interpret. Two weeks worth of crime data for a beat or ward can easily number in the hundreds. Placing limits on the data helps ensure better performance.

Q. Why is the search distance limited to 1/2 mile?
A. A half mile is 4 city blocks which should be sufficient for examining crime around an address, school, or park. This was also done to reduce the load placed on the web server.

Q. Why are searches back-dated a week?
A. After an investigation is performed by the preliminary investigator, each case is sent to the Detective Division for further review. During this review, additional information may be obtained and crime classifications may change. The one-week delay allows case classifications to become more stable after detectives have reviewed the case. However, additional information learned at any time may continue to impact case classifications, as explained below.

Q. Why do crime classifications change?
A. As additional facts about a case are learned, they can cause the crime classification initially assigned by the preliminary investigator to change. Cases can even be unfounded, which means that further investigation reveals that a crime did not occur at all. (For example, a citizen returns from vacation and finds her lawn mower missing, which she reports to the police. Later, she learns that her son borrowed the lawn mower, and that it was not stolen: no crime occurred.) Due to these changes, long-term comparisons of crime information obtained from this web site will not be reliable.

Q. Why don't all crimes show up on the map?
A. Chicago's street network is extremely complex. With continual construction of new homes and buildings, it is possible that a location from which an incident is reported may not exist on the current maps. If this occurs, it will not be properly geocoded. However, the maps are constantly updated.

Q. Does sharing this information jeopardize police operations?
A. In most situations the information shown is based upon reported incidents which have already occurred. Sharing this information will not have an effect on day-to-day police operations. During covert operations, especially involving narcotics, information may not be recorded until the operation has been completed. This will insure the safety of the officers involved as well as prevent suspects from being made aware of confidential activity.

Q. Why do I need to turn off my web browser pop-up blocker?
A. This site uses pop-up windows for several reasons. The primary reason is to maximize the size of the map image by removing unnecessary toolbars, address bars and button bars from the browser window. The Back button on a web browser does not function properly with CLEARMAP and removing it eliminates a potential source of error. Additionally because the application uses framesets it makes printing difficult so, the Print feature opens a map image in a pop-up window. The MapLink feature and the Table printing feature also take advantage of opening new browser windows.

Note: Most modern pop-blockers whether native to the web browser or part of an add-on toolbar like Google or Yahoo allow you to add this website (http://gis.chicagopolice.org) to a list of websites that are allowed to use pop-ups. We recommend taking advantage of this capability to keep your pop-up blocker on while enabling CLEARMAP to function properly.

Q. Why do I need to zoom in close to view crime?
A. The crime points aren't shown on the map until only a few city blocks are shown in the window unless the user searches for crime around a specific address, school, or park. This is done to improve performance and make the map easier to read. Showing all crime at a citywide scale would be useless for the viewer. The map would be nothing but a blob of overlapping points.

Q. I have more questions about crime on my beat.
A. Attend your beat meeting and talk to your beat officers! Visit our web site for meeting locations and dates: http://www.cityofchicago.org/police or call Chicago's Non-Emergency telephone number, 3-1-1.

Q. Can I just pan around the Map viewing crime?
A. Yes, you just need to be zoomed in close enough and if you've used a Search By function like Address click the MapView button to remove any geographic restriction. See the question below.

Q. What does the MapView button do? Why is it important?
A. The MapView button located beneath the map on the right side of the Search By: section is used to remove any geographic restriction you may have placed on the map. For example, when you Search By: Address a red circle is drawn around the address and only those crimes that fall within the circle are shown. If you click the MapView button the circle is removed and you will see any incidents that occurred outside the circle that are within the map window. You can then freely pan around the map viewing crime. If you zoom too far out on the map without a geographic restriction the points will disappear. Just zoom in closer and they will reappear.

The MapView button removes all the other geographic restrictions like beat, district, ward, community area, school, park, and polygons drawn using the Draw Shape tool. If you see an area bound by a red line clicking MapView will remove the line and the geographic restriction.

Q. Is there a quick why to change the date range?
A. By default the mapping application uses the most current two week date range. Remember, the earliest date you can search is one week prior to the current day. To quickly jump back to the previous two weeks, select the date drop down on the right (the TO date) and scroll down and select the first date not highlighted in blue. The date on the left (the FROM date) will automatically adjust to a two week period. Then click the Apply! button next to the date range and the map will update.

The blue highlighting is there to help you quickly see the two week range. There is a different color for the first seven days as compared to the last seven days. You can of course search a shorter time period than two weeks.

Q. How does the Draw Shape tool work?
A. The Draw Shape tool (left side- middle) allows you to draw your own geographic boundaries instead of using an address, beat, ward, etc. Click Draw Shape to activate the tool. The tool has 3 methods.

1) Double-click once on the map creating a Point and a circle with a radius of 660 ft. (1 city block) will be drawn and points inside of it shown.

2) Make a Line Selection by single clicking once, moving the mouse and double-clicking to complete the line.  Points on either side of the line will appear inside a box.

3) Create a Polygon by single clicking several times and finishing with a double-click. Do NOT try and close the polygon the last double-click will close the polygon. For example, to create a triangle (3 sides) click once, move mouse, click once, move mouse, double-click. The triangle will be completed and the points inside shown. Important: when using this tool do not draw lines that overlap, if you do the tool won’t work.  You are limited to a polygon with 10 vertices

If you make a mistake, click the Draw Shape button and start over.

Q. How does the MapLink feature work?
A. The MapLink feature enables people to share a common map view using an encoded URL link. This can be useful for facilitating a discussion about crime in a particular area. When you press the MapLink button a new web page is open with the URL link and a list of the query parameters. The query parameters include the date range, location, and visible crime types.  The best way to share this information is to copy the entire page into an email. A quick way to do that on a Windows PC’s is to use Ctrl A (Select All), Ctrl C (Copy), open the email page and press Ctrl V (Paste). Copying the entire page lets your email receiver know where this information came from (gis.chicagopolice.org) and what parameters you had selected when you created the link. Give it a try and remember the receiver needs to be using a supported web browser.