Issue 53

Mapping Election Results with MapViewer 6

Introduction

The recent national election in the United States highlighted the use of thematic maps and cemented the terms red state and blue state in the American lexicon. The commonly-shown map of election results by state is easy to make in MapViewer 6. This article will quickly step through making this map, and will then examine some alternatives to address an issue that some people raised after the election.

Creating the Red/Blue Map of Election Results

The type of map where the state is filled with a color based on a data value is known in MapViewer as a hatch map. This type of map is also sometimes called a choropleth, from the Greek words choros, meaning "place", and plethos, meaning "magnitude" or "value". Like any thematic map in MapViewer, you need two things to make one - a set of boundary objects (the states) and a data file containing the values to be displayed. The objects and the data are linked by the Primary ID (PID) field.

MapViewer comes with many boundary files, some in the Samples folder underneath the installation directory and more on the CD. For our election map, we will use the file US50alb.gsb from the Samples folder for the state outlines. The state area objects have the two-letter state abbreviation as the PID. A data file will need to be created with the election results. It needs a PID column and a data column indicating which party won that state. We can use a value of 1 for Republican and 2 for Democrat. The data file I created for this example is available atwww.goldensoftware.com/public/scripts/surfer8/bil2grd3.bas.

The data needed to make a red/blue election hatch map
has a column that matches the PIDs of the states and a column with a
numeric value that represents the winner in each state.

Do the following steps to make the hatch map:

1. In a new, blank map, go to Map | Thematic Maps | Hatch Map.
2. In the Import Boundary File dialog, choose the file Us50alb.gsb from MapViewer's Samples folder. Check the boxes for Append image and Specify import options at the bottom and clickOpen.
3. In the GS Boundary Import Options dialog, make sure the box for Areas to curves is NOT checked and click OK.
4. The settings will probably default correctly in the Import Options, but make sure that Create PID is checked and that it is coming from the Primary field. The correct PID is necessary for the thematic map to be created.
   
   
   

   It's important for the PID attribute to be populated from the boundary file.

5. In the Open Data File dialog, select the data file shown above and click Open.
6. Make the following settings in the Hatch Map dialog:
   • PID: = Column A: PID
   • Variable: = Column B: Party
   • Number of classes: = 2
   • Classification method: = Equal intervals
   • Draw type: = Hatched area
   • Give the first class a fill color of red and the second blue.
   
   
   
   

   Check these settings in the Hatch Map dialog.

7. Then, click OK to create the hatch map
   
   
   

   2004 Presidential election results.

Is this map misleading?

After this type of map started being published, some questioned whether it accurately represented the results. This type of map displays data by area, while the vote is by population. Since some large states have small populations and vice versa, coloring in the states by area does not show the number of votes. Excluding Alaska and Hawaii - which are resized and relocated in this map - the red states comprise approximately 75% of the area and the blue states 25%, while the vote totals were considerably closer than this.

One way to address this issue is to use an option on the hatch map to show a filled circle or square for each state rather than filling in the whole area. To do this, go to the map properties and change the Draw type to Hatched Circle. Although this helps by ignoring the area of the states, it also ignores the population and treats each state equally.

The same map with hatch circles.

Use a Dorling Cartogram to show population

MapViewer 6 has a new type of map called a Dorling Cartogram that can be used to replace the original state area objects with circles that are sized according to a data value - in our case, the population. The circles are moved to try to maintain connectivity with neighbors while maintaining the approximate locations of the states.

This Dorling Cartogram replaces the state shapes
with circles sized according to the population.

Now that we have circles sized according to population, we can convert the cartogram to a base map, choosing to keep the circles rather than the original shapes, and then use them as the base for our red/blue hatch map. To do this:

1. Go to Map | Thematic Maps | Cartogram Map.
2. In the Dorling Cartogram Map dialog, check the box for Keep cartogram after switching to base map, uncheck Keep original areas with cartogram after switching to base map, and click OK.
3. Go to Map | Base Map to convert the cartogram into a base map.
4. Go to Map | Thematic Map | Hatch Map to create the red/blue hatch map using the cartogram circles. Use the same data file and settings as shown above when creating the first hatch map.

An election map based on cartogram circles can show
the results based on population rather than by area.

The hatch map made using the population-based cartogram circles more accurately reflects the election results. Although the states have been replaced by circles, their relative locations are maintained and the voting patterns are still evident.