Monday, December 12, 2016

What GIS can do for crime analysts

I originally wrote this post for a software company’s blog in 2014. This company was bought out and recently their blog and website have been removed from the web permanently. I am reposting it here for posterity. 

One thing I wanted to accomplish this year in these blog posts was to provide some useful information for those crime analysts who might be starting out, especially those who have little or no formal training. While at many medium to larger agencies, they are fortunate to be able to hire trained, experienced crime analysts, this is not always the case at small agencies. I’ve met quite a few analysts who got their start when their boss walked into their office where they were working as a clerk or secretary and gave them the duties of a crime analyst.

Obviously, this is not the ideal way to get your start as a crime analyst. But the reality is that even small, cash strapped agencies realize the value a crime analyst brings to their efforts to make their community safer.

In this post we’re going to look at an important tool for a crime analyst, a Geographic Information System or as it’s most commonly known, GIS. In simplest terms, GIS is a software application that lets you create maps. However, unlike an application like Google Earth, a GIS lets you conduct sophisticated analysis of large datasets and geographic elements. In his book GIS for Public Safety, Dr. Joel Caplan describes GIS this way:
A geographic information system (GIS) is a computer software application for managing, editing, analyzing and displaying data which is spatially referenced to the Earth. GIS is a tool with which data can be layered with base maps that represent the landscape of the area where the data is associated. Base maps could represent the street network, buildings, census tracts, or local landuse patterns. These data can be represented as individual layers, displayed as separate entities, or be combined with other layers to be displayed together.

Where GIS really shines is the ability to pull different layers into a map and use these layers together. Here’s an example.

A few years ago at my agency we wanted to redesign our Beat Areas. We had some significant growth since the last time our Beat Areas were drawn up and there was some concerns that the current Beats were no longer even. One challenge with Beat Areas is trying to balance size and workload for the officers that work them. The situation you don’t want is to end up with one officer taking a disproportionate amount of Calls or another ending up with a Beat Area so large he couldn’t realistically cover it during his shift. In this project we decided that we would try to strike a balance with three different variables.

  1. Calls for Service
  2. Street Network Length
  3. Geographic Size

I added several years of geocoded Calls for Service data to a map that also contained layers for the Street Network and current Beat Area boundaries. I could then analyze the current Beat Area boundaries to determine the number of Calls for Service, the length of the Street Network and geographic size of these areas. I then used the current Beat Areas as a starting point and adjusted the boundaries of each Beat to try and get areas where all of these variables were as close to equitable as possible.

This geographic analysis used several hundred thousand Calls for Service, several hundred miles of Street Network and over one hundred square miles of land area. This type of analysis would be near impossible to do without GIS. Just pushing a couple hundred thousand pins on a map would take way more time than most of us have (not to mention pushpins!). GIS makes this type of analysis pretty easy.

If you want to learn more about what GIS can do for crime analysts, here’s a couple of helpful resources:

The National Institute of Justice’s Mapping and Analysis for Public Safety program. They also have an excellent, and free book Mapping Crime: Principle and Practice that you can read or download. It might be worth reading the book to see what GIS can do for a crime analyst and to learn some of the basic terms.

ESRI is the leading provider of GIS software. They have dedicated resources for GIS in Public Safety. You can find that here. They have excellent software and support. However, excellence is not free.

There’s even an Open Source GIS project called GRASS if you’re really budget constrained. The GRASS software is free. You can learn more here.

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