Visual Literacy & Maps

When thinking about election maps, especially showing results from US Presidential elections, we most commonly think of a map showing states colored either red or blue... something like this: 

The problem with choropleth, or shaded area maps like these is that while technically accurate, they do not show the full picture of population, and therefore votes. In this map, visual weight is based on the size of each state, rather than on the number of votes. This means that large, sparsely populated states like Montana with its 3 electoral votes appear to be more prominent on the map than geographically smaller, but more densely populated states such as Massachusetts, which casts 11 electoral votes.  So if we wanted to know who won the 2016 presidential election, this map isn't very helpful. However, it does reveal geographic voting patterns that can help us see clusters of Democratic-leaning states in New England and on the West Coast. There are some things we could do to improve this map, like adding text about the number of electoral college votes each state casts, but that still requires significant effort on the part of the map reader to parse. A bar chart would be more appropriate for showing the number of electoral votes cast for each candidate. 

A popular alternative to a choropleth map, is a cartogram, like this one created by Mark Newman, from the University of Michigan:

This cartogram weights the size of each state by the number of electoral votes cast. Now we can see that the sparsely populated western states shrink, while the more populated northeast becomes larger. The visual weight of red vs blue is more accurate, but this type of map can be difficult to read if the shape and location of areas is too distorted. However, we maintain the benefit of being able to see geographic voting patterns. 

It might not be surprising that these various types of maps appeal to different audiences. President Trump famously hung a choropleth map of 2016 election results in the West Wing, while Democrats may tend to prefer a cartogram or dot density map. While they look completely different, these two maps use the same data, and are technically both "correct"! 

Choropleth map in the West Wing vs. Dot Density map made by Ken Field.

Of course, you should also be on the lookout for blatantly fake maps. One of the easiest ways to spot these is if they don't cite their data source. 

See the next tab for articles about different ways to map elections, and the benefits and drawbacks of each.