2004 Election: The Red States

For the first mini-project, your assignment is to reproduce the following graphic that appeared in the New York Times. You are to turn in the plot and the code used to create the plot.

For your map of the United States, you have available to you the following data:

• Election results for each county
  • state name, county name (in lower case)
  • Votes for Bush
  • Votes for Kerry

Plot Description

We use Wilkinson's grammar to describe the plot.

• DATA: lead = bushVote - kerryVote
  centroid lattitude = lattitude of county center computed from the map function
  centroid longitude = longitude of county center computed from the map function
• TRANS: sqrt(abs(lead))
• FRAME: lattidue * longitude
• SCALE: interval
• GUIDE:
  • Main title: Election 2004 the Final Tally
  • Subtitle: How Much Each County counted
  • Subtitle: Popular Vote, By County
  • Marker: Largest vote margin for Kerry,...
  • Marker: Largest vote margin for Bush,...
  • Marker: Second largest vote margin for Bush,...
  • Legend: blue and red circles for 1,000 10,000 50,000 100,000 500,000
  • Marker: county and state boundaries
• GRAPH: circles(radius proportional lead, color by winner, i.e. bushVote > kerryVote)) exclude the counties in New York City

• FRAME: lattitude * longitude
• SCALE: interval
• GUIDE: New York City label and pointer
• COORD: translate to Atlantic Ocean
• GRAPH: circle(radius proportional lead of all counties in NYC, color by winner, i.e. bushVote > kerryVote))

Handy R packages and functions

• The three packages, maps, mapdata, and mapproj contain functions for drawing maps. The map function is simple to use. One call, map("usa") draws a map of the united states, map("state") includes the state boundaries, and map("county") includes county boundaries.

• Additional text and symbols can be added to maps with the text() and symbols() functions. To convert latitude and longitide to the plotting coordinates, you can use the mapproject() function.

• The package RColorBrewer contains Cindy Brewer's color palettes. The function display.brewer.all produces a window containing the spectrum of colors.

  The functions rgb, hsv, gray and rainbow provide additional ways of generating colors.

  The palette function alows you to set the palette of colors. Other color-related functions that may be of interest are colors palette palette colors(), terrain.color(), and col2rgb().

  Additional Things to Keep in Mind

  • COUNTY CENTERS -- Most counties are polygonal in shape, and the center of the polygon may be of interest to you. To find the vertices of these polygons, you can call the map function (with specification of particular arguments) and save the output in an R object. The function below takes as input the output from the map project and returns a list of matrices, one for each polygon. The matrices contain the coordinates of the vertices of the polygon, and the row names are the names that map assigns to each polygon.

    
    polys = function(mapObj) {
      n = length(mapObj$x)
    # The polygon vertices are delimited by an NA entry
      breaks = which(is.na(mapObj$x))
      starts = c(1, breaks+1)
      ends = c(breaks -1, n)
      result = list()
      if (length(starts) == length(mapObj$names) ) {
          for (i in 1:length(starts)) {
            poly = matrix(c(mapObj$x[starts[i]:ends[i]],
                          mapObj$y[starts[i]:ends[i]]), ncol = 2, byrow = FALSE)
            result[[ mapObj$names[i] ]] = poly
          }
      }
      result
    }
    
    

    Note that the map package has a function to compute the centroid of a polygon given its vertices.

    Also note that it is important to keep track of the counties and be sure that you properly match the data for a county with its county center.