Locate the position of CRAN mirror sites on a map using Google Maps

August 5, 2009

(This article was first published on One R Tip A Day, and kindly contributed to R-bloggers)

Inspired by this post (suggested here by the always useful Revolutions blog), I attempted to plot the position of CRAN mirrors on a map taking advantage of the nice R package RgoogleMaps (check the dependencies!). Below the code:

# download.file("http://www.maths.lancs.ac.uk/~rowlings/R/Cranography/cran.gml",destfile="cran.gml")
cran.gml <- xmlInternalTreeParse("cran.gml")
# Create a data.frame assembling all the information from the gml file
Name <- sapply(getNodeSet(cran.gml, "//ogr:Name"), xmlValue)
Country <- sapply(getNodeSet(cran.gml, "//ogr:Country"), xmlValue)
City <- sapply(getNodeSet(cran.gml, "//ogr:City"), xmlValue)
URL <- sapply(getNodeSet(cran.gml, "//ogr:URL"), xmlValue)
Host <- sapply(getNodeSet(cran.gml, "//ogr:Host"), xmlValue)
Maintainer <- sapply(getNodeSet(cran.gml, "//ogr:Maintainer"), xmlValue)
CountryCode <- sapply(getNodeSet(cran.gml, "//ogr:countryCode"), xmlValue)
lng <- as.numeric(sapply(getNodeSet(cran.gml, "//ogr:lng"), xmlValue))
lat <- as.numeric(sapply(getNodeSet(cran.gml, "//ogr:lat"), xmlValue))
cran.mirrors <- data.frame(Name, Country, City, URL, Host, Maintainer, CountryCode, lng, lat)
# cran.mirrors <- cbind(getCRANmirrors(), lng, lat) ## alternatively
# Define the markers:
cran.markers <- cbind.data.frame( lat=cran.mirrors$lat, lon=cran.mirrors$lng,
size=rep('tiny', length(cran.mirrors$lat)), col=colors()[1:length(cran.mirrors$lat)],
char=rep('',length(cran.mirrors$lat)) )
# Get the bounding box:
bb <- qbbox(lat = cran.markers[,"lat"], lon = cran.markers[,"lon"])
num.mirrors <- 1:dim(cran.markers)[1] ## to visualize only a subset of the cran.mirrors
maptype <- c("roadmap", "mobile", "satellite", "terrain", "hybrid", "mapmaker-roadmap", "mapmaker-hybrid")[1]
# Download the map (either jpg or png):
MyMap <- GetMap.bbox(bb$lonR, bb$latR, destfile = paste("Map_", maptype, ".png", sep=""), GRAYSCALE=F, maptype = maptype)
# Plot:
png(paste("CRANMirrorsMap_", maptype,".png", sep=""), 640, 640)
tmp <- PlotOnStaticMap(MyMap,lat = cran.markers[num.mirrors,"lat"], lon = cran.markers[num.mirrors,"lon"],
cex=1, pch="R",col=as.numeric(cran.mirrors$Country), add=F)

## Hosts from Italy
maptype <- c("roadmap", "mobile", "satellite", "terrain", "hybrid", "mapmaker-roadmap", "mapmaker-hybrid")[4]
num.it <- row.names(cran.mirrors[cran.mirrors$CountryCode=="IT",])
# Get the bounding box:
bb.it <- qbbox(lat = cran.markers[num.it,"lat"], lon = cran.markers[num.it,"lon"])
# Download the map (either jpg or png):
ITMap <- GetMap.bbox(bb.it$lonR, bb.it$latR, destfile = paste("ITMap_", maptype, ".png", sep=""), GRAYSCALE=F, maptype = maptype)
#ITMap <- GetMap.bbox(bb.it$lonR, bb.it$latR, destfile = paste("ITMap_", maptype, ".jpg", sep=""), GRAYSCALE=F, maptype = maptype)
# Plot:
png(paste("CRANMirrorsMapIT_", maptype,".png", sep=""), 640, 640);
tmp <- PlotOnStaticMap(ITMap,lat = cran.markers[num.it,"lat"], lon = cran.markers[num.it,"lon"],
cex=2, pch="R",col="dodgerblue", add=F)
# tmp <- PlotOnStaticMap(ITMap,lat = cran.markers[num.it,"lat"], lon = cran.markers[num.it,"lon"],labels=as.character(cran.mirrors[cran.mirrors$CountryCode=="IT",]$Host),col="black", FUN=text, add=T)

CAVEAT: To reproduce the example you need the gml file you can download from here , a  Google account and a Google Maps API key. Here you can sign up for a free API key.

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