Pie charts on GIS maps using R

Question

I'm an R user and have been using libraries like gistools and rgdal. I notice that ArcGIS appears to have features to add pie charts onto the maps themselves. (For example, if I have a map of the US, I can add a pie chart to each state). However, a quick search of gistools and rgdal documentation does not show any function to add such features.

Is there any easy way to add pie charts onto maps in R?

Answer 1

There are several options depending on which R package you want to use. The following links should give you some insights into some of the possibilities available.

• Using mapplots and specifically the add.pie function (see this worked example and map below)
• Using the rworldmap package as described here
• Using the plotGoogleMaps package - see example here

(Map Sourced from: http://www.molecularecologist.com/2012/09/making-maps-with-r/)

Answer 2

I might add here: add.pie() is a function of mapplots.

In the documentation of "mapplots" draw.pie() is the recommended function to use

Be careful if you combine the package RgoogleMaps and "mapplots". The coordinates are scaled as soon as you set a "Zoom" parameter. Here an example of an arbitrary data frame:

map1=GetBingMap(center=c(47.619048,-122.35384),zoom=15,apiKey=apiKey, 
                  verbose=1, destfile="Seattle.png") 
PlotOnStaticMap(map1)

if you add multiple pie charts on the map, this will only give you a cluster in the middle of your plot! (Note df$values is a matrix containing at least two columns corresponding the size of a slice)

library(mapplots)
draw.pie(z=df$values, x=df$lat, y=df$long, radius = 20, col=c(alpha("orange", 0.6), alpha("blue", 0.6)), labels="")

Hence you will have to rescale your pie chart coordinates first (use the map and zoom factor as above):

xy <- LatLon2XY.centered(map1,df$lat, df$long, zoom = 15)

library(mapplots)
draw.pie(z=df$values, x=xy$newX, y=xy$newY, radius = 20, col=c(alpha("orange", 0.6), alpha("blue", 0.6)), labels="")