(This article was first published on

**R-english – Freakonometrics**, and kindly contributed to R-bloggers)There was an interesting map on reddit this morning, with a visualisation of latitude and longituge of where people live, on Earth. So I tried to reproduce it. To compute the density, I used a kernel based approch

> library(maps) > data("world.cities") > X=world.cities[,c("lat","pop")] > liss=function(x,h){ + w=dnorm(x-X[,"lat"],0,h) + sum(X[,"pop"]*w) + } > vx=seq(-80,80) > vy=Vectorize(function(x) liss(x,1))(vx) > vy=vy/max(vy) > plot(world.cities$lon,world.cities$lat,) > for(i in 1:length(vx)) + abline(h=vx[i],col=rgb(1,0,0,vy[i]),lwd=2.7)

For the other axis, we use a miror technique, to ensure that -180 is close the +180

> Y=world.cities[,c("long","pop")] > Ya=Y; Ya[,1]=Y[,1]-360 > Yb=Y; Yb[,1]=Y[,1]+360 > Y=rbind(Y,Ya,Yb) > liss=function(y,h){ + w=dnorm(y-Y[,"long"],0,h) + sum(Y[,"pop"]*w) + } > vx=seq(-180,180) > vy=Vectorize(function(x) liss(x,1))(vx) > vy=vy/max(vy) > plot(world.cities$lon,world.cities$lat,pch=19) > for(i in 1:length(vx)) + abline(v=vx[i],col=rgb(1,0,0,vy[i]),lwd=2.7)

Now we can add the two, on the same graph

To

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