Great Maps with ggplot2

February 2, 2012

(This article was first published on » R, and kindly contributed to R-bloggers)

The above map (and this one) was produced using R and ggplot2 and serve to demonstrate just how sophisticated R visualisations can be. We are used to seeing similar maps produced with conventional GIS platforms or software such as Processing but I hadn’t yet seen one from the R community (feel free to suggest some in the comments). The map contains three layers: buildings, water and the journey segments. The most challenging aspect was to change the standard line ends in geom_segment from “butt” to “round” in order that the lines appeared continuous and not with “cracks” in, see below.

I am grateful to Hadley and the rest of the ggplot2 Google Group for the solution. You can see it here. From this point I layered the plots using the geom_polygon() command for the buildings and water bodies and my new function geom_segment2() for the journey segments- these were simply the start and end latitudes and longitudes for each node in the road network and the number of times a cyclist passed between them. I have included the code below

#Code supplied by james cheshire Feb 2012
#load packages and enter development mode

#if your map data is a shapefile use maptools

#create GeomSegment2 function
GeomSegment2 objname <- “geom_segment2″
draw if (is.linear(coordinates)) {
return(with(coord_transform(coordinates, data, scales),
segmentsGrob(x, y, xend, yend, default.units=”native”,
gp = gpar(col=alpha(colour, alpha), lwd=size * .pt,
lty=linetype, lineend = “round”),
arrow = arrow)

geom_segment2 “identity”, position = “identity”, arrow = NULL, …) {
GeomSegment2$new(mapping = mapping, data = data, stat = stat,
position = position, arrow = arrow, …)

#load data stlat/stlong are the start points elat/elong are the end points of the lines
lon names(lon)<-c(“stlat”, “stlon”, “elat”, “elong”, “count”)

#load spatial data. You need to fortify if loaded as a shapefile
water built

#This step removes the axes labels etc when called in the plot.
xquiet yquiet<-scale_y_continuous(“”, breaks=NA)
quiet<-list(xquiet, yquiet)

#create base plot

#ready the plot layers
pbuilt<-c(geom_polygon(data=built, aes(x=long, y=lat, group=group), colour= “#4B4B4B”, fill=”#4F4F4F”, lwd=0.2))
pwater<-c(geom_polygon(data=water, aes(x=long, y=lat, group=group), colour= “#708090″, fill=”#708090″))

#create plot


To leave a comment for the author, please follow the link and comment on their blog: » R. offers daily e-mail updates about R news and tutorials on topics such as: Data science, Big Data, R jobs, visualization (ggplot2, Boxplots, maps, animation), programming (RStudio, Sweave, LaTeX, SQL, Eclipse, git, hadoop, Web Scraping) statistics (regression, PCA, time series, trading) and more...

If you got this far, why not subscribe for updates from the site? Choose your flavor: e-mail, twitter, RSS, or facebook...

Comments are closed.

Search R-bloggers


Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)