ArcMap - Cartograms Tutorial

This tutorial was expanded and adapted from Kerski, J.J.. (2009). Exploring Data Using Cartograms within ArcGIS Desktop.  Redlands, CA: ESRI.  Retrieved October 5, 2009, from ESRI GIS Education Community: http://blogs.esri.com/Info/blogs/gisedcom/archive/2009/10/16/exploring-data-using-cartograms-within-arcgis-desktop.aspx.

Copy Data Files to the Desktop

To complete this tutorial, you will need to copy the Cartograms folder from the O:\envstudies\GIS Tutorials folder to the desktop of your computer.  If you have done this already, skip to the next section, Start a New Map Document.

1. Go to the Start menu
2. Click My Computer
3. Double click on the O: Drive
4. Folders are listed alphabetically by department.  Double click on the envstudies folder.
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5. Double click on the GIS Tutorial folder.  Inside you will see the Cartograms folder.
6. Right click on the CartogramsTutorial folder, and choose the Copy option.
7. Close the GIS Tutorial window.
8. Right click anywhere in the blank, blue space on the Desktop of your computer.  Choose the Paste option.  You should now see the CartogramsTutorial folder on your Desktop.

Install the Cartograms Tool

If you are working on a laptop or a computer in your office, you will need to download and install the ArcScript cartogram tool created by Tom Gross in the ESRI Applications Prototype Lab before beginning this tutorial.  Download the files at

http://arcscripts.esri.com/details.asp?dbid=15638

and follow the installation instructions in the ReadMe file.  Once you’ve installed the software, restart your computer.

Open the USPop2007 Map Project 

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1. Open ArcMap.
2. Click the An existing map; button.
3. In the Browse area, highlight Browse for maps…
4. Click OK.  The Open dialog box should appear.
5. In the Look In: pull down menu, choose Desktop. 
6. Highlight the CartogramsTutorial folder.  Click OK.
7. Highlight the USPop2007.mxd map project.  Click OK.

Repair the Data Sources for your Map Layers

ArcMap sets file paths to find the data for each of your map layers.  Because you moved the data files from the O:\envstudies drive to your Desktop, the file paths that ArcMap stored are no longer accurate.  You can easily repair the file paths.  This is something you will need to do each time you want to use a Map Project you’ve copied or moved from one location to another.

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1. Right click on the 2007 Population by County map layer.  In the pop-up menu, choose Data → Repair Data Source.  The Data Source dialog box will appear.
2. In the Look In: menu of the Data Source dialog box, navigate to the CartogramsTutorial folder on the Desktop.   If you do not see a path to the Desktop, you can find it in I:\YourUserName\Desktop. 
3. Double click on the CartogramsTutData.mdb personal geodatabase.
4. Highlight the Counties file and click Add.  The Counties file was renamed to 2007 Population by County in the ArcMap Table of Contents for the Map Project, but retains its original name in the Personal Geodatabase.

The Data Frame should now contain a map of the continental United States, with the 2007 Population by County indicated in an orange color scheme.

Add the Cartograms Tool to ArcToolbox

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1. Open ArcToolbox by clicking on the ArcToolbox button .
2. Right click on the white space inside the ArcToolbox menu.  Choose New Toolbox.  A new, unnamed toolbox will appear in the Toolbox menu.  Name it Cartograms.
   
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3. Right click on the title of the new Cartogram toolbox.  Choose Add → Tool.
4. Check the box next to the Cartograms option.  Click OK.

The Cartogram → Create a cartogram (Gastner-Newman method) tool will appear. 

Use the Cartograms Tool

1. Open the Cartograms Tool and double click on Create a cartogram.  The Create a cartogram dialog box will appear.
2. Fill in the values for these fields:
   1. Original Polygon Features – Choose 2007 Population by County
   2. Value Field of the Original Features – Choose POP07_SQMI
   3. Allow the default Output Cartograms Features
   4. Uncheck the box next to Sum the Values for each repeated ID
   5. Scroll down and make sure that the box is checked next to Copy the Original Polygon Features table to the Output Cartogram Features table.

Your dialog box should look like this:


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1. Click OK.

A Cartogram will be created in the new layer. Cartograms distort map shapes to emphasize specified values from underlying map data. In this case, shape of the U.S. map will be distorted to reflect the population density of each area, since you chose to use the POP07_SQMI value from the attributes of the 2007 Population by Counties Map Layer as your Value Field for analysis. Areas with greater population densities will be larger than those with smaller population densities. This new layer will not be Symbolized – meaning that the color scheme indicating population density has not been transferred from the 2007 Population by County Map Layer.