(Nearly) Automated Crime Mapping
By Tim Dees
MapPoint is a Microsoft product that is not part of the usual complement of programs in its Office packages, but readily accepts data from programs like Access and Excel. Last time, we demonstrated how to plot the locations of an address list by importing the list into MapPoint. In that example, all of the data points plotted had the same identifier, as they were not otherwise broken out on the list that was created in Excel. If your crime map showed only one type of offense or was for only one period of time, then this would be an acceptable solution by itself. But agencies usually depict either multiple crime types or time periods on a single map in order to show trends and clusters, and for that we need to use multiple symbol types.
As long as we’re going to use multiple symbols, we might as well have symbols that are meaningful. MapPoint has an assortment of large and small dots and pushpins of varying colors, but it also provides for the use of custom symbols for each mapped event. We’re going to use a portion of our fictitious data set of “crimes” in San Jose, CA, to plot car thefts and burglaries using distinctive symbols.
The first step is to add to the existing data set a field indicating what crime occurred at each address. This is done by adding a fifth column to the existing list of addresses, and entering a crime into that fifth column for each record. To make the data entry process simple, the first 24 records or so were listed as auto thefts, while the next 47 were burglaries, and 24 more were designated as robberies. Had the data been entered in a more random order, sorting would have been as simple as using the Data|Sort command in Excel. The data doesn’t even need to be sorted, as MapPoint will map each data point according to the event regardless of the order of the list.
Once that list has been created and saved, we open MapPoint to a new file. Pressing Control-W activates the Data Mapping Wizard, which offers more options than the Data Import Wizard used last month. The Data Mapping Wizard guides us through a series of steps necessary to map the data points from the Excel file. The first of these is to choose the type of map we want to make. This will be a multiple symbol map, the others being better suited for other data types. The next screen in the wizard asks for the data to map. The option to import data is selected. The next two screens ask for the location of the data file, and then the “Finish” button is clicked.
Choosing “Crime” as the field that distinguishes one address from another, we see that MapPoint offers to plot each type of crime with a different color dot. However, there is also an option to choose a custom symbol. You can use any graphic symbol on your computer, but it has to be in bitmap (*.bmp), icon (*.ico) or cursor (*.cur) format, and can’t be over 128 x 128 pixels in size. In practice, smaller symbols, between 10 and 30 pixels on a side, work better. To create the symbols used in this example, I took some stock Microsoft clip art (downloadable for free from Microsoft’s Clip Gallery), opened it in Windows Paint (included in all Windows installations under “Accessories”), used the Image|Stretch/Skew feature to shrink the graphics to about 10% of their original sizes, and then saved them in bitmap format. It was these symbols, a sports car and a safe, that I used as custom symbols for auto theft and burglary. For comparison purposes, a yellow dot was left to show robberies.
When the custom symbol is selected, it will appear in the array of dots of pushpins, above the others. The user needs to click on this to bind that symbol to the event. When the symbols have been chosen, the only remaining step is to click the “Finish” button, and the crime map is complete.
You might look at the map and feel that leaving the crimes represented by colored dots is less confusing, and you might be right. The ability to use symbols to represent mapped events is shown to illustrate the capabilities of the program. In any event, mapping crimes with MapPoint is certainly easier and more accurate than the manual method, and as many events as the user cares to illustrate can be combined on one map. By changing the structure of the data sheets that the crime information is drawn from, any combination of map data can be displayed, and far more cheaply than with the manual method or using an expensive dedicated crime mapping program.
MapPoint won’t do everything. Patrol zones, unless they are very large, would be difficult to delineate with the software, as the smallest geographic area that MapPoint will identify with distinctive shading is the area covered by a zip code. But, if you keep, or can export, your data in Access or Excel, MapPoint will plot your geographic events quickly and inexpensively.
Tim Dees is a former officer who writes and consults about applications of technology in law enforcement. He can be reached at (509) 585-6704 or by e-mail at firstname.lastname@example.org.