Choropleth maps are a very common visualization to show some measurement or statistical variable using shaded regions. They’re most appropriate for showing ratios, proportions, or percentages rather than absolute raw numbers.
If you’d like to create your own choropleth map there are several online tools available that will do the job for you without you having to be a cartographer. Carto DB is my current favorite and it will allow you up to 5 data sets for free currently. If you need more than that, they have paid plans available.
If you want to go the total free route, Google Fusion Tables is another option. Choropleth maps created with Fusion tables can look a bit basic and simplistic unless you’re a more advanced user, but if you’re looking for a fairly simple solution with no cost, it might just be the ticket. In this article, I’ll give a quick overview of creating basic choropleth maps using Google Fusion Tables.
First of all, below you can see examples of several choropleth maps I’ve created and embedded. The first two are examples that depict absolute values and the third example is a better use of a choropleth map that shows the number of solar installations per square mile for each state. The data set I used for these examples and for this tutorial can be found on the Open PV Project website.
[Each of these example maps is interactive. Hover over any state in a map to see the state name and the corresponding value for that state.]
Absolute Number of US Solar Installations by State
Absolute Solar Capacity in MW
Solar Installations per 1,000 Square Miles
Ok, so how to go about creating one of these maps.
1. Get the Data
The first step of course is to get your data. As mentioned earlier, I got my data from the Open PV Project website and put it into a Google Docs spreadsheet. I also added the area in square miles for each state to the data set in order to add some context to the visualization.
I downloaded my spreadsheet to my computer as a .csv file, since .csv files are a very common file format for creating visualizations and you can create them from your favorite spreadsheet software.
2. Create a New Fusion Table
Open Google Drive in your browser of choice and click on the big red Create button in the top left corner and then select the Fusion Table icon. If you don’t see the Fusion Table icon, click on the Connect more apps link to add Fusion Tables as an option that you can work with.
3. Load Your Data
If you’ve got the .csv file on your computer, choose the file and upload it to Fusion Tables
Fusion Tables will import your data and walk you through the initial process with a simple dialog window.
4. Geocode Your Data
Next Fusion Tables needs to make sense of the map areas you’re using in your data set. In this example, the names of each state are in one column and this column will be used to map each state and its data with the corresponding area shape of that state. Go to the menu and select File > Geocode.
Another dialog box will pop open. Click the button that says “Begin geocoding.”
It’s worth mentioning here that you the tool can be very particular about the areas that you’re trying to geocode. If you use state abbreviations, or a state name is misspelled, Fusion Tables will not be able to geocode the data so make sure your data is clean. This applies to country names as well if you’re creating a world choropleth map with countries.
5. Create the Map
Once your data is geocoded, you’ll see your data in a spreadsheet-like format again. Now however, the states that have been geocoded are no longer highlighted in yellow. If you’re like I was when I was first figuring out Fusion Tables, you’ll want to click on the Map of State tab. But, if you do, you’ll just get frustrated. The latest version of Fusion Tables doesn’t include the ability to make choropleth maps, or intensity maps as Fusion Tables calls them. But, the previous version, known as Classic, does have the ability. So, you need to switch to the old version to make your choropleth/intensity map (for now anyway. I’m sure Google will add the functionality eventually in the new version).
To switch to classic view, go to the Help menu and select “Back to Classic look.”
Once in the classic mode, go to Visualize > Intensity Map.
What you see next might annoy you as it doesn’t look anything near what you’d expect it to. It’s just a map of the world with the US shaded green.
But, notice the form at the top of the page, specifically, the field that says Area and currently has the word World in it. Select that word and start typing United States. When you do, you’ll see that you can then select United States from a sort of drop down menu. Important! Double Click on the word United States. If you don’t double click on it, it doesn’t seem to want to take.
Once you double click on “United States” the map will change…
6. Share Your Map
Most likely you’ll want to share your new creation with the world as an embeddable, interactive map. To do that, click the button Get embeddable code. In doing so, you’ll get another pop-up window where you can copy the link or get the embed code. Keep in mind that in order for the rest of the world to see your awesome creation, you’ll have to change the privacy settings to Public to allow the rest of the world to see it.
7. Try It Out. Experiment. Have Fun! Enjoy!