Building a Geospatial Information System

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Web Map Showing Chicago Neighborhood Crime Trends and Statistics

In this post I provide a behind the scenes look and quick explanation of how I prepared and mapped Chicago crime data using a Content Management System (CMS) specially designed for GIS data. The system allows you to create, manage, collaborate and share your maps, apps and data with groups you setup or via social media. The hallmark of any CMS is access control, the ability to create user roles, set permissions, and enable better use of resources by making content available to those who need them most. I attempt to demonstrate these concepts in this short blog. At the end of the blog, there is a link to the crime web map where you can access and use the resources through the CMS where you can then modify the map for your own purposes.

Web Map Showing Chicago Neighborhood Crime Trends and Statistics

I created this map several years ago as one of three submissions to a technology contest called ‘Apps for Metro Chicago’ (#A4MC on Twitter), no I didn’t take any of the prize money but I learned a lot and had some fun participating in the contest. The web map is built with ESRI’s ArcGIS cloud-based technology. The crime data is from the Chicago Police Department’s crime data API, which is downloadable from the City of Chicago’s open data portal. There are approximately 5 million records represented on this map.

Data Preparation

Before I was able to create the web map, I had to prepare the data for mapping at the neighborhood level. I used professional GIS desktop software to do this, figure 1. This phase took about a month. I started with an Excel spreadsheet, performed many spatial overlay queries on the data to allocate each crime record to its corresponding Chicago Neighborhood.

Geospatial Information System

Further data analysis created new fields to store the neighborhood crime totals by type of crime. These fields were used for displaying the totals on the web map’s pie chart in figure 2.

Map Design

The next phase was linking the data to and designing the web map, figure 2. The web map is highly interactive, using popup window graphs to show crime trend data over a ten year period in popup window 1, and a click-able pie chart showing the total number of crimes by type in each neighborhood in popup window 2 (hint: look for the small left/right facing arrows). The map itself is designed as a choropleth thematic map that color codes polygons to convey information about the area, neighborhoods in this case (a thematic map is a type of map especially designed to show a particular theme connected with a specific geographic area). The map’s numeric values representing the total number of crimes in a neighborhood consist of four value intervals displayed on the map in varying shades of blue.

Demo Map

Geospatial Information System

Now try out the map for yourself. Follow the link below and then the instructions to open the CMS’s built-in map viewer. After the map opens, you’ll be able to use the map as is, or modify it, creating your own mashup by adding data and maps shared by others. Look for the ‘Modify Map’ link in the upper right-hand corner. Start by changing the basemap choosing one of the included aerial/satellite imagery backgrounds, topographic or street maps. The topographic basemap includes authoritative content provided by a global online community. Next, you can add additional data by searching for and adding new data layers (for example Census demographic data, business locations, crime indexes, etc.) to the map. You can even add your own data from an Excel spreadsheet and change map symbols through the built-in map viewer. You can then share your modified version of the map with groups within your organization or using social media. You can even use your new version of the map embedded in your own website or blog. Look for the share link then the Embed in Website link. Here you can configure the settings for your own mapping application as I’ve done, shown below.

View: Web Map Showing Chicago Neighborhood Crime Trends and Statistics
Note: clicking this link will take you away from this website.

Web mapping application

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