GIS Cookbook: Recipe - Making a Choropleth map  
Keywords: Spatial analyisis, choropleth map, color symbology
Category: Data Analysis
Software: ArcView 3.2

Problem: How do I make a choropleth map, so I can see pattterns and analyze them.

Description: A choropleth map is a map that uses different colors to show different values over space. This is very helpful to look at different values displayed over space.

Scenario:
Ever since the work of John Snow and his mapping of Cholera cases, mapping cases and frequencies of diseases can help to find sources and cures. One of the major research topics of the 20th century is the search for an understanding of cancer. It helps researchers in the subject to know where the cases of cancer are the highest. In this scenerio, we are going to look at the state of New Mexico the cancer statistics for each county. Once finish we can look at and analyse the information and compare it to other choropleth maps.

Methodology:
1) Open ArcView and add the layer/shapefile you want to work with.

Your starting attribute


2) Click on the shapefile in the table of contents, making it active, and then select Theme ->Table This will display the . If it is not, and you need to add it from an external source, see the recipe Joining a table (3.x) Make sure to note the name of the column you are going to display.

Open your attribute table


Your shapefiles attribute table


3) Double click on the shapefile in the table of contents and your will appear

Double click on your theme/shapefile to bring up the Legend Editor


4) In the second dialogue box in your legend editor, change the Legend Type: from Single Symbol to

Select graduated color


Graduated color selected


5) Now, in the third dialogue box Classification Field: select the Attribute column from your shapefile that you wish do display in different categories, by highlighting it.

Change to the attribute you want to map by


6) The preorganized classes for your choropleth map will appear.


Your prearranged classes will appear


7) Now, within the window you can edit the colors (color ramps), number of classes (Classify button), your class intervals (double click on the numbers themselves) and even the types of classifications(advanced, classify button) you can use to display your map. To obtain the best results, it is best to use trial and error when it comes to these details.

You can easily change your color scheme


9) When the settings are tuned to your liking click Apply and then Ok

10) Your choropleth map will appear on your map window.

Your Choropleth map the higher the number or darker the color the higher rate of cancer in that county
Authored by: Benjamin N. Sprague Modified: 9/11/03


Copyright © 2002-2014 by Regents of University of California, Santa Barbara
Cookbook: Ben Sprague, Ethan Sundilson, Carlin Wong, Sam Ying