Mapping U.S. Presidential Elections
by David Zubenko Above is a map by Robert J. Vanderbei, Princeton University, showing how the popular vote total in the 2012 election was actually quite close. Counties that heavily favored one candidate are shaded red or blue, respectively. Counties where the vote was close are colored various shades of purple based on which candidate won and by how much.
INTRODUCTION Few things capture the imagination of Americans like Presidential elections. Each contest is proceeded by months, even years of primaries, debates, and endless campaigning. Wall to wall coverage is provided by every form of media from newspapers and television to blogs and websites. All of them, however, feature maps. Maps to show information about individual states and counties. Maps to show the candidates’ travel schedule. Maps to show where political ads are being aired. This project will take a look at three types of these maps and their uses: choropleth, proportional symbol, and cartogram. Below is a brief summary of each map type.
CHOROPLETH “Choropleth maps represent quantitative data that is aggregated to areas” (Geography 160: Mapping our Changing World). In Presidential elections this most often means some sort of information is being shown at the state or county level. However, these units can be anything that, “divides the whole territory into distinct areas” (Geography 160: Mapping our Changing World) These areas are divided into “classes” that are all shaded the same color. In the case of ordered (numerical) data each class is usually shaded according to a “sequential” color scheme, however, any color scheme that clearly shows the distance between one extreme and the other is acceptable. Sometimes this is a divergent color scheme that highlights, “an important midrange or critical value of ordered data as well as the maximum and minimum data values. Two contrasting dark hues converge in color lightness at the critical value” (Geography 160: Mapping our Changing World). Choropleth maps can also show categorical data which is then shaded according to a qualitative color scheme that distinctly shows the difference between each category. A common example is Presidential election maps that are shaded red (Republican) and blue (Democrat). Choropleth maps are best used for representing derived quantities such as densities, averages, rates, and percents. Below is an example of a choropleth map.
Courtesy of Geography 160: Mapping our Changing World
PROPORTIONAL SYMBOL Proportional symbol maps use a symbol (usually a circle), to show the magnitude of something. These types of maps are best used for showing total numbers or values, also known as counts. An example is the population of an area. A variation on a proportional symbol map is a pie chart map where, “a circle is scaled proportionally to some total and the size of wedges within the circle is scaled to depict a proportion of a total for two or more sub-categories” (Geography 160: Mapping our Changing World). Below is an example of a proportional symbol map that shows unemployment percentages by state in 2000.
Courtesy of Geography 160: Mapping our Changing World
CARTOGRAMS “A cartogram can be considered a special case of proportional symbol mapping. But, in this case the “symbol” that is scaled in proportion to a data magnitude is the geographic area for which data are aggregated” (Geography 160: Mapping our Changing World). While they do many things well, the disadvantage of cartograms is that they are only useful if the viewer is familiar with the normal geographic layout of the area.
Courtesy of Adam Cole
Courtesy of Jimmy Margulies
THE REPORT This report contains examples of the map types described above as they relate to Presidential elections. It is divided into three sections based on the three sources the maps came from. For the most part each section corresponds with a particular map type. When reviewing individual maps the following criteria were applied: What kind of data is being shown? What is the data source? Is it reliable? If not, are there better sources? What is the key decision that was made in the making of each map? How appropriate is the map for the data it is trying to show? How was the data classified? What symbology choices were used? What is the overall eectiveness of the map?
Courtesy of David Horsey
ELECTORAL COLLEGE RESULTS (CHOROPLETH) What Data is Being Shown? These maps show the states won by George Washington (top, green; New York, Rhode Island, and North Carolina had not joined the Union yet) and Barack Obama (blue) and Mitt Romney (red). What is the data source? ffIs it reliable? This data came from the Electoral College, certified by Congress, and is a reliable and appropriate source of information.
What was the key decision in the making of each map? The key decision in making these maps was to show which candidate won each state on a standard United States map. This does not take into account things like margin of victory or the relative importance of a state based on the number of votes it has in the electoral college. This additional information would make the maps more useful.
How appropriate is the map for what it is trying to show? Although choropleth maps typically don’t show numerical totals, in this case it is an appropriate map since it is also showing which candidate won each state. This is categorical data which can be shown on a choropleth map. How was the data classified? The data was classified by which candidate won each state.
What symbology choices were used? A qualitative color scheme was used for both maps. How effective are the maps? Despite their shortcomings, these maps are effective because they are a basic way to visually communicate the results of a presidential election, and perhaps more importantly, are what the public has come to expect. These maps can be found at: www.270towin.com
2012 ELECTION - NEW YORK TIMES (CHOROPLETH + PROPORTIONAL SYMBOL) What Data is Being Shown? The top map is a choropleth map showing the margin of victory at the county level in percent. The bottom map is a proportional symbol map that shows the margin of victory at the county level in votes What is the data source? fffIs it reliable? The data source was the popular vote in the 2012 election. It is reliable.
What was the key decision in the making of each map? For the choropleth map the key decision was to show a derived quantity (in this case percent). For the proportional symbol map it was to show the result in votes, a numerical total. Both of these decisions let the maps play to their strengths. How appropriate is the map for what it is trying to show? Both maps are appropriate since, as mentioned, they are showing the kind of data they are best suited for.
How was the data classified? In the choropleth map the data is classified by an equal interval scale. The proportional symbol map classifies the data by its raw value. What symbology choices were used? For the choropleth map a sequential color scheme was employed for both candidates. For the proportional symbol map circles of various sizes were used.
How effective are the maps? All in all both maps are effective. If you are not familiar with proportional symbol maps you may find it confusing that it is showing the results in votes and not as a percent, however, that is the appropriate format for that map type. These maps can be found at: http://elections.nytimes.com/ 2012/results/president
2012 ELECTION - MARK NEWMAN, UNIVERSITY OF MICHIGAN (CARTOGRAM) What Data is Being Shown? The first map is proportioned to show the relative importance of each state based on how many votes it has in the electoral college. The second map shows what counties have the most influence by adjusting the size of the county to its population. The final map is showing how close the vote was at the county level using the same “Purple America” system as the map on the cover page.
What is the data source? fffIs it reliable? These maps are based on reliable data such as the popular vote in the 2012 election and how many votes a state has in the electoral college.
How appropriate is the map for what it is trying to show? The overall purpose of these maps is to show the relative importance of one unit to another. Therefore, a cartogram was an appropriate map choice.
What was the key decision in the making of each map? Cartograms only work if the viewer is familiar with the map they are based on, and this was the key decision in the making of these maps.
How was the data classified? Cartograms are maps that adjust to fit numerical data, therefore, the data was not “classified”. This is in contrast to choropleth maps where the map stays the same and the data is classified to fit it.
What symbology choices hwere used? The first two maps feature a qualitative color scheme, while the last map features a divergent color scheme. How effective are the maps? For what they are trying to show I feel these maps are very effective. In particular they classify the data very well by being specific, and are therefore more accurate. These maps can be found at: www-personal.umich.edu/~mejn/election/2012
References “270towin.com.” (2013). Retrieved April 7, 2013 from http://www.270towin.com Cole, Adam. (2012). “A Campaign Map, Morphed By Money.” Retrieved April 7, 2013 from http://www.npr.org/blogs/itsallpolitics/ 2012/11/01/163632378/a-campaign-map-morphed-by-money Geography 160: Mapping our Changing World (2013). Chapter 3. Retrieved April 20, 2013, from ssssss https://cms.psu.edu/section/content/Default.asp? WCI=pgDisplay&WCU=CRSCNT&ENTRY_ID=E0285A2CA2254B12AC515771DA4C0499
Horsey, David. (2012). Retrieved April 20, 2013 from http://editorialcartoonists.com/cartoon/display.cfm/116241/ Margulies, Jimmy. (2012). The Cagle Post. Apple Maps. Retrieved April 20, 2013 from http://www.cagle.com/2012/09/apple maps-2/ #.UXREdb9TNUR Newman, Mark. (2012). “Maps of the 2012 US presidential election results.” Retrieved April 7, 2013 from http://www personal.umich.edu/~mejn/election/2012/ New York Times (2012). Election 2012. Retrieved April 7, 2013 from http://elections.nytimes.com/2012/results/president Vanderbei, Robert J. (2012). “2012 Presidential Election Results.” Retrieved April 7, 2013 from http://www.princeton.edu/~rvdb/JAVA/ election2012/