Iowa precinct shapefile example

iowa-shapfiles-example.R

library(rgdal)
library(broom)
library(ggplot2)

setwd("~/work/data/iowa-election-results/")

# Download the shapefile data if we don't already have it
if (!file.exists("./data")) {
    dir.create("./data")
    if (!file.exists("./data/pcts_04172014_0908am.zip")) {
        dataUrl <- "https://sos.iowa.gov/shapefiles/Statewide%20Precinct%20Layer/pcts_04172014_0908am.zip"
        download.file(dataUrl, destfile="./data/pcts_04172014_0908am.zip", method="libcurl")
        library(utils)
        unzip("./data/pcts_04172014_0908am.zip", exdir="./data")
    }
}

# Read the shapefile
precincts <- readOGR(dsn="data/pcts_04172014_0908am", layer="Precincts041714")

# Extract a subset, for example Senate District 10
s10_precincts <- subset(precincts, Senate_Dis == '10')

# Plot the precincts
precincts_df <- tidy(s10_precincts)
p <- ggplot(precincts_df) + aes(long, lat, group=group)
p <- p + geom_polygon(fill="purple") + geom_path(color="white") + coord_equal()
p <- p + ggtitle("Iowa Senate District 10")
p