Yesterday evening, I was walking in Budapest, and I saw some nice map that was some sort of Otto Neurath style. It was hand-made but I thought it should be possible to do it in R, automatically.

A few years ago, Baptiste Coulmont published a nice blog post on the package osmar, that can be used to import OpenStreetMap objects (polygons, lines, etc) in R. We can start from there. More precisely, consider the city of Douai, in France,

The code to read information from OpenStreetMap is the following

library(osmar)
src <- osmsource_api()
bb <- center_bbox(3.07758808135,50.37404355, 1000, 1000)
ua <- get_osm(bb, source = src)

We can extract a lot of things, like buildings, parks, churches, roads, etc. There are two kinds of objects so we will use two functions

listek = function(vc,type="polygons"){
nat_ids <- find(ua, way(tags(k %in% vc)))
nat_ids <- find_down(ua, way(nat_ids))
nat <- subset(ua, ids = nat_ids)
nat_poly <- as_sp(nat, type)}

listev = function(vc,type="polygons"){
  nat_ids <- find(ua, way(tags(v %in% vc)))
  nat_ids <- find_down(ua, way(nat_ids))
  nat <- subset(ua, ids = nat_ids)
  nat_poly <- as_sp(nat, type)}

For instance to get rivers, use

W=listek(c("waterway"))

and to get buildings

M=listek(c("building"))

We can also get churches

C=listev(c("church","chapel"))

but also train stations, airports, universities, hospitals, etc. It is also possible to get streets, or roads

H1=listek(c("highway"),"lines")
H2=listev(c("residential","pedestrian","secondary","tertiary"),"lines")

but it will be more difficult to use afterwards, so let’s forget about those.

We can check that we have everything we need

plot(M)
plot(W,add=TRUE,col="blue")
plot(P,add=TRUE,col="green")
if(!is.null(B)) plot(B,add=TRUE,col="red")
if(!is.null(C)) plot(C,add=TRUE,col="purple")
if(!is.null(T)) plot(T,add=TRUE,col="red")

Now, let us consider a rectangular grid. If there is a river in a cell, I want a river. If there is a church, I want a church, etc. Since there will be one (and only one) picture per cell, there will be priorities. But first we have to check intersections with polygons, between our grid, and the OpenStreetMap polygons.

library(sp)
library(raster)
library(rgdal)
library(rgeos)
library(maptools)
identification = function(xy,h,PLG){
  b=data.frame(x=rep(c(xy[1]-h,xy[1]+h),each=2),
               y=c(c(xy[2]-h,xy[2]+h,xy[2]+h,xy[2]-h)))
  pb1=Polygon(b)    
  Pb1 = list(Polygons(list(pb1), ID=1))
  SPb1 = SpatialPolygons(Pb1, proj4string = CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0"))
  UC=gUnionCascaded(PLG)
  return(gIntersection(SPb1,UC))
}

and then, we identify, as follows

whichidtf = function(xy,h){
  h=.7*h
  label="EMPTY"
if(!is.null(identification(xy,h,M))) label="HOUSE"
if(!is.null(identification(xy,h,P))) label="PARK"
if(!is.null(identification(xy,h,W))) label="WATER"
if(!is.null(identification(xy,h,U))) label="UNIVERSITY"
if(!is.null(identification(xy,h,C))) label="CHURCH"
return(label)
}

Let is use colored rectangle to make sure it works

nx=length(vx)
vx=as.numeric((vx[2:nx]+vx[1:(nx-1)])/2)
ny=length(vy)
vy=as.numeric((vy[2:ny]+vy[1:(ny-1)])/2)
 plot(M,border="white")
 for(i in 1:(nx-1)){
     for(j in 1:(ny-1)){
         lb=whichidtf(c(vx[i],vy[j]),h)
         if(lb=="HOUSE") rect(vx[i]-h,vy[j]-h,vx[i]+h,vy[j]+h,col="grey")
         if(lb=="PARK") rect(vx[i]-h,vy[j]-h,vx[i]+h,vy[j]+h,col="green")
         if(lb=="WATER") rect(vx[i]-h,vy[j]-h,vx[i]+h,vy[j]+h,col="blue")
         if(lb=="CHURCH") rect(vx[i]-h,vy[j]-h,vx[i]+h,vy[j]+h,col="purple")      
     }}

As a first start, we us agree that it works. To use pics, I did borrow them from https://fontawesome.com/. For instance, we can have a tree

 library(png)
 library(grid)
 download.file("https://f.hypotheses.org/wp-content/blogs.dir/253/files/2018/05/tree.png","tree.png")
 tree <- readPNG("tree.png")

Unfortunatly, the color is not good (it is black), but that’s easy to fix using the RGB decomposition of that package

 rev_tree=tree
 rev_tree[,,2]=tree[,,4]

We can do the same for houses, churches and water actually

 download.file("https://f.hypotheses.org/wp-content/blogs.dir/253/files/2018/05/angle-double-up.png","angle-double-up.png")
 download.file("https://f.hypotheses.org/wp-content/blogs.dir/253/files/2018/05/home.png","home.png")
 download.file("https://f.hypotheses.org/wp-content/blogs.dir/253/files/2018/05/church.png","curch.png")
water <- readPNG("angle-double-up.png")
 rev_water=water
 rev_water[,,3]=water[,,4]
 home <- readPNG("home.png")
 rev_home=home
 rev_home[,,4]=home[,,4]*.5
 church <- readPNG("church.png")
 rev_church=church
 rev_church[,,1]=church[,,4]*.5
 rev_church[,,3]=church[,,4]*.5

and that’s almost it. We can then add it on the map

 plot(M,border="white")
 for(i in 1:(nx-1)){
   for(j in 1:(ny-1)){
     lb=whichidtf(c(vx[i],vy[j]),h)
     if(lb=="HOUSE")  rasterImage(rev_home,vx[i]-h*.8,vy[j]-h*.8,vx[i]+h*.8,vy[j]+h*.8)
     if(lb=="PARK") rasterImage(rev_tree,vx[i]-h*.9,vy[j]-h*.8,vx[i]+h*.9,vy[j]+h*.8)
     if(lb=="WATER") rasterImage(rev_water,vx[i]-h*.8,vy[j]-h*.8,vx[i]+h*.8,vy[j]+h*.8)
     if(lb=="CHURCH") rasterImage(rev_church,vx[i]-h*.8,vy[j]-h*.8,vx[i]+h*.8,vy[j]+h*.8)     
   }}

Nice, isn’t it? (as least as a first draft, done during the lunch break of the R conference in Budapest, today).