plotting pie graphs on map in ggplot

Three years later this is solved. I’ve put together a number of processes together and thanks to @Guangchuang Yu’s excellent ggtree package this can be done fairly easily. Note that as of (9/3/2015) you need to have version 1.0.18 of ggtree installed but these will eventually trickle down to their respective repositories.

I’ve used the following resources to make this (the links will give greater detail):

1. ggtree blog
2. move ggplot legend
3. correct ggtree version
4. centering things in polygons

Here’s the code:

load(url("http://dl.dropbox.com/u/61803503/nycounty.RData"))
head(ny); head(key)  #view the data set from my drop box

if (!require("pacman")) install.packages("pacman")
p_load(ggplot2, ggtree, dplyr, tidyr, sp, maps, pipeR, grid, XML, gtable)

getLabelPoint <- function(county) {Polygon(county[c('long', 'lat')])@labpt}

df <- map_data('county', 'new york')                 # NY region county data
centroids <- by(df, df$subregion, getLabelPoint)     # Returns list
centroids <- do.call("rbind.data.frame", centroids)  # Convert to Data Frame
names(centroids) <- c('long', 'lat')                 # Appropriate Header

pops <-  "http://data.newsday.com/long-island/data/census/county-population-estimates-2012/" %>%
     readHTMLTable(which=1) %>%
     tbl_df() %>%
     select(1:2) %>%
     setNames(c("region", "population")) %>%
     mutate(
         population = {as.numeric(gsub("\\D", "", population))},
         region = tolower(gsub("\\s+[Cc]ounty|\\.", "", region)),
         #weight = ((1 - (1/(1 + exp(population/sum(population)))))/11) 
         weight = exp(population/sum(population)),
         weight = sqrt(weight/sum(weight))/3
     )


race_data_long <- add_rownames(centroids, "region") %>>%
    left_join({distinct(select(ny, region:other))}) %>>%
    left_join(pops) %>>%
    (~ race_data) %>>%
    gather(race, prop, white:other) %>%
    split(., .$region)

pies <- setNames(lapply(1:length(race_data_long), function(i){
    ggplot(race_data_long[[i]], aes(x=1, prop, fill=race)) +
        geom_bar(stat="identity", width=1) + 
        coord_polar(theta="y") + 
        theme_tree() + 
        xlab(NULL) + 
        ylab(NULL) + 
        theme_transparent() +
        theme(plot.margin=unit(c(0,0,0,0),"mm"))
}), names(race_data_long))


e1 <- ggplot(race_data_long[[1]], aes(x=1, prop, fill=race)) +
        geom_bar(stat="identity", width=1) + 
        coord_polar(theta="y") 

leg1 <- gtable_filter(ggplot_gtable(ggplot_build(e1)), "guide-box") 


p <- ggplot(ny, aes(long, lat, group=group)) +  
    geom_polygon(colour="black", fill=NA) +
    theme_bw() +
    annotation_custom(grob = leg1, xmin = -77.5, xmax = -78.5, ymin = 44, ymax = 45) 



n <- length(pies)

for (i in 1:n) {

    nms <- names(pies)[i]
    dat <- race_data[which(race_data$region == nms)[1], ]
    p <- subview(p, pies[[i]], x=unlist(dat[["long"]])[1], y=unlist(dat[["lat"]])[1], dat[["weight"]], dat[["weight"]])

}

print(p)