How to Create a Choropleth Map for Your Research Paper

Step 1: Rank and organize the data

You will write a research paper on a topic of your choice, and will create a choropleth map to support your thesis statement and/or one of the arguments in your paper. The paper must be written from a geographical perspective. This is easy to forget given that geography overlaps with other disciplines. Connecting your paper with ideas from the course is an excellent way to demonstrate understanding of concepts learned in this course. Just adding a map to the end of the paper is not sufficient to declare your paper geographical. Many other disciplines use maps to express a certain idea.

Once you have acquired a suitable blank map, you are ready to map your data. Follow the steps outlined here:

a. Rank the data from low to high (i.e. organized the counties or states, again according to your circumstances, from the lowest to the highest). Applying this step to the sample European data, this is what you do:

Albania $4,250

Bosnia $4,880

Bulgaria $7,470

Belgium $41,860

Austria $45,230

b. Calculate your range and intervals for your data. I recommend you stick with an equal interval. I know what you are thinking, “what is an equal interval?” Again, good question! In an equal interval the entire range of values is equally divided by the number classes you choose. Let me give you an example using the European data we have been using so far. To obtain your range, simply take the lowest value (in our example that would be $4,250 for Albania) and subtract it from the highest value (this would be $45,230 for Austria): $45,230 - $4,250 = $40, 980. So this is our range (i.e. $40,980). Now we take that value and divided by the number of classes we want to have in our legend. I recommend, you do no less than 3 and no more than 6. So, assuming we do 4 classes, we would take our range and divided by the number of classes (in this example 4): $40,980/4 = $10,245. This figure now represents the “interval” for every class. So now you create your four classes of “equal intervals”:

$4,250 to $14,495

$14,496 to $24,740

$24,740 to $34,985

$34,986 to $45, 230

To double check this step, simply take the lowest value in every interval and subtract it from its corresponding high value, they should all give you the same figure (i.e. $10,245) with the exception of the last one.

c. Group your counties or states. This is where you ‘group’ every county or state according to their value, and where this value falls in the intervals or classes you just created. Continuing with our European Example:

$4,250 to $14,495 Albania, Bosnia, Bulgaria

$14,496 to $24,740 No country

$24,740 to $34,985 No country

$34,986 to $45, 230 Belgium, Austria

Note that the second and third intervals or classes have no countries that is because in the small sample I selected we have values in the extreme (i.e. in the lower end and the upper end) and nothing in the middle. This is somewhat uncommon, but not completely out of the ordinary, so if this happens in your data, no need to worry. After all, in this example I selected two high income and two low income countries in Europe, so this indicates a lot of income inequality between these four nations.

d. Create symbols for the intervals. You must only use one color and different tones of the same color. In other words, if you choose red, you can use a light tone of red (i.e. pink) for the first interval (i.e$4,250 to $14,495), and a successive darker tone of red for the following intervals until you reach the last one (the one with the highest values $34,986 to $45, 230), in which case you use the darkest tone of red.