Let’s say you have some data that’s coded by geographic area. For example, you might have a table showing the number of COVID cases per 100,000 people county by county in Massachusetts. It might look like this:
fips state county cases/100,000 deaths/100,000 25001 Massachusetts Barnstable 133 1 25003 Massachusetts Berkshire 170 6 25005 Massachusetts Bristol 2623 139 25007 Massachusetts Dukes 814 0 25009 Massachusetts Essex 1062 54 25011 Massachusetts Franklin 121 11 25013 Massachusetts Hampden 2565 181 25015 Massachusetts Hampshire 330 16 25017 Massachusetts Middlesex 760 39 25019 Massachusetts Nantucket 1912 18 25021 Massachusetts Norfolk 732 57 25023 Massachusetts Plymouth 910 49 25025 Massachusetts Suffolk 1478 56 25027 Massachusetts Worcester 638 30
How do you make your own choropleth from your data? There are a few ways.
- One is to use Tableau Public, a free service from the Tableau data visualization service online.
What’s in your data?
The first column is a FIPS county code. Each code uniquely identifies a county in the USA. This code comes in handy for making choropleths: all sorts of county-by-county data carries FIPS codes identifying the counties. In particular, we’ll need map data showing the county outlines.
The next four
What do you need?
To get all this to work you need these programs and data.
- Your data, stored in a CSV file.
- Map data containing the boundary of each county along with its FIPS code. This comes from the US Census Bureau’s Cartographic Boundary Shapefiles, via Michael Bostock’s TopoJSON project on Github. In his us-atlas repository he has translated the Shapefiles to the TopoJSON format. That’s what you need to make the map your choropleth. There are plenty of other sources for boundary data in TopoJSON format, but this project has organized it nicely for displaying county-by-county maps.
- An Integrated Development Environment (IDE). I like Webstorm. Many people like Microsoft Visual Studio Code.