Creating Inset Map with ggplot2

According to wiki.GIS.com one of the reason for using inset map is to provide a reference for an area for unfamiliar readers.  Inset map is also considered a great asset for cartographers.  Most of the GIS software available in the market have a provision for non-cartographer and beginners to create inset map. However, for R users who are into making maps, creating inset map is a bit challenging. Thanks to the post of Pascal Mickelson and Scott Chamberlain which gave users like me a guide on how to create inset map in R using ggplot2. Below is an example of map with inset created using R.

	##################################
	# Creating Inset Maps in ggplot2 #
	##################################
	library(ggplot2)
	library(raster)
	library(gridExtra)
	ph0<-getData("GADM", country="PHL", level=0) # download PHL level 0 map for ucdavis site
	phl<-getData("GADM", country="PHL", level=2) # download PHL level 2 map for ucdavis site
	mrdq<-(phl[phl$NAME_1=="Marinduque",]) # subset province of Marinduque from PHL map
	munnames<-coordinates(mrdq) # get center coordinates of municipalities of Marinduque
	munnames<-data.frame(munnames) # convert matrix format munnames object to data.frame
	munnames$label<-mrdq@data$NAME_2
	# Extent rectangle for inset map
	pol<-data.frame(xmin=121.7,xmax=122.2 ,ymin=13 ,ymax=13.7)
	# Main Map
	p1<-ggplot()+geom_polygon(data=mrdq, aes(long+0.008,lat-0.005, group=group), fill="#9ecae1")+
	geom_polygon(data=mrdq, aes(long,lat, group=group), colour="grey10",fill="#fff7bc")+
	geom_text(data=munnames, aes(x=X1, y=X2,label=label), size=3, colour="grey20")+
	coord_equal()+theme_bw()+xlab("")+ylab("")+
	scale_x_continuous(breaks=seq(121.8,122.2, 0.1), labels=c(paste(seq(121.8,122.2, 0.1),"°E", sep="")))+
	scale_y_continuous(breaks=seq(13.2,13.6, 0.1), labels=c(paste(seq(13.2,13.6, 0.1),"°N", sep="")))+
	theme(axis.text.y =element_text(angle = 90, hjust=0.5))
	#Inset
	p2<-ggplot()+geom_polygon(data=ph0, aes(long,lat,group=group),colour="grey10",fill="#fff7bc")+
	coord_equal()+theme_bw()+labs(x=NULL,y=NULL)+
	scale_x_continuous(breaks=seq(117.5,125, 2.5), labels=c(paste(seq(117.5,125, 2.5),"°E", sep="")))+
	scale_y_continuous(breaks=seq(5,20, 5), labels=c(paste(seq(5,20, 5),"°N", sep="")))+
	geom_rect(data = pol, aes(xmin = xmin, xmax = xmax, ymin = ymin, ymax = ymax), alpha=0, colour="red", size = 1, linetype=1)+
	theme(axis.text.x =element_blank(),axis.text.y= element_blank(), axis.ticks=element_blank(),axis.title.x =element_blank(),
	axis.title.y= element_blank())
	png(file="mrdq.png",w=1800,h=1800, res=300)
	grid.newpage()
	v1<-viewport(width = 1, height = 1, x = 0.5, y = 0.5) #plot area for the main map
	v2<-viewport(width = 0.3, height = 0.3, x = 0.86, y = 0.28) #plot area for the inset map
	print(p1,vp=v1)
	print(p2,vp=v2)
	dev.off()

view raw Inset.r hosted with ❤ by GitHub