Roll-your-own choropleth map with free tools
November 12th, 2009 by analyticjournalism

Nathan, honcho at FlowingData,  has put together a fine tutorial on making a choropleth map using free tools.  This is one bookmark you will want to save.

How to Make a US County Thematic Map Using Free Tools

Posted: 11 Nov 2009 10:57 PM PST

There are about a million ways to make a choropleth map. You know, the maps that color regions by some metric. The problem is that a lot of solutions require expensive software or have a high learning curve…or both. What if you just want a simple map without all the GIS stuff? In this post, I'll show you how to make a county-specific choropleth map using only free tools.

The Result

Here's what we're after. It's the most recent unemployment map from last week.

Unemployment in the United States

Step 0. System requirements

Just as a heads up, you'll need Python installed on your computer. Python comes pre-installed on the Mac. I'm not sure about Windows. If you're on Linux, well, I'm sure you're a big enough nerd to already be fluent in Python.

We're going to make good use of the Python library Beautiful Soup, so you'll need that too. It's a super easy, super useful HTML/XML parser that you should come to know and love.

Step 1. Prepare county-specific data

The first step of every visualization is to get the data. You can't do anything without it. In this example we're going to use county-level unemployment data from the Bureau of Labor Statistics. However, you have to go through FTP to get the most recent numbers, so to save some time, download the comma-separated (CSV) file here.

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