Choropleth Counties

on April 4, 2011

Choosing how to display data is often the most difficult part of the data visualization process. Would a bar chart be superior to a pie? Perhaps a scatter would tell more than two bar charts? One of the most difficult of these choices is between filled maps (choropleth) and shapes.

Choropleth maps have several advantages. First, they avoid overlap and because of it they are usually very neat and beautiful. Choropleth maps also tend to make it easy to spot trends geographically, like the clusters of major cities in the household income map above.

However, shapes also have some interesting traits. First of all, it can be much easier to spot small outliers. You may notice how Los Alamos County, NM stands out in the bottom view, but is nearly invisible in the top view. Shapes also have the relative advantage of not distorting by size, because they give equal weight to each mark. This can be frustrating though, since they can overlap, as in the eastern US with this map.

Regardless of your choice, it is relatively easy to create both types of map in Tableau. For the choropleth map, you will need a polygon file, but once you have that it is a simple data blend away. If you have an interest, you can download the US counties polygon file used to make this map, courtesy of Alan Smithee.


Great work. Choropleth map certainly distinguishes each region, giving better understanding of the data.

I am mapping trade balance of one country with different countries around the world. How do you change from the regular round shape to chropleth?

Good post, Ross. Short, sweet and informative:)

To the above commenter, Abby: in order to display information as a choropleth in Tableau you need to have downloaded an external "polygon file" for the geo-area that you wish to display and then upload that file as your geo-background inside Tableau. In the above example, Ross used a polygon file for US Counties (which is a commonly needed file). For your case, you will need to find/create polygon files for the countries that you want to include in your analysis.

Hope this helps!

Good Post Ross,
I would like to see Tableau integrate the polygon data into the software. It is intimidating to do it manually as a rookie with the software, and linking tables also can be confusing when trying to do other visualizations.

The basic fact of these types of visualizations is that internal and external clients like (even express deep love for) them, which drives additional usage of the tool which should drive additional licenses.

I would like to see this at the existing geographic levels, but I would imagine some folks would like to see it a congressional districts too.

hey guys, I've a question...I import vector maps from Inkscape to excel (directly via copy-paste), I then ungroup everything and finally get a set of freeform shapes - countries.
some freeform-countries consist of several separate regions (ex. New Zealand, 2 islands but one freeform is not a grouped object, it is one freeform)
question: how can I split these shapes in excel (ex. I want to have two freeforms for New Zealand) Of course I can do it in Inkscape and then import to excel, but I'd want to know whether it is possible directly in excel.

In the Shapes map, it would be nice if you can control which shape 'floats' on top in the case of overlapping shapes. I would want the red shapes to surface on top, for example. It would be a type of sorting or ordering. I wish Tableau can do this when rendering the Shapes map chart.

What would the next step be to implement this map? I am a bit of a novice and am not sure how I would leverage the information from the file you provided into Tableau. I have my set of data and am able to get a shape map like the lower visual above, but am clueless on how to create something like the upper map. Do I need to combine this file with my original data set or would I upload it as another data set and use it in conjunction? I appreciate any help and the more detailed the answer the better.