Question

I would like to plot a geographical map with n numbers of squares according to the frequency of a disease within a county. Like this one here:

But I couldn’t figure out how to do this with R or qGIS.
Thanks for y’all help.

Answer 1

First write a little function called ‘stackbox’ that plots (using “rect”) the squares for the stack in the right place.

Here’s the first line of that function:

stackbox <- function(x,y,n,size,maxheight=5){

• where ‘size’ is the height and width of the boxes, and ‘maxheight’ lets you have a stack that is 5 high or 10 high or whatever.

Then call that function for every county that has cases.

Where exactly were you stuck in the process?

Here’s the function in full:

stackbox <- function(x,y,n,size,maxheight=5,...){
  stackheight = seq(0,n,by=maxheight)
  stackheight=diff(unique(c(stackheight,n)))

  for(col in 1:length(stackheight)){
    xl=rep(x+(col-1)*size,stackheight[col]) - (length(stackheight)/2)*size
    yb=y+size*((1:stackheight[col])-1) - (max(stackheight)/2)*size
    xr=xl+size
    yt=yb+size
    rect(xl,yb,xr,yt,...)
  }
}

Example:

plot(1:10)
for(i in 1:10){
 stackbox(i,i,i,3,size=.1,col="red",border="white")
}

To do this on a map, you need the sp and maptools packages, and a shapefile or other geospatial data source that has your data in it:

africa=readShapeSpatial(file.path(mapLib,"africa.shp"))
plot(africa,border="gray")
coords=coordinates(africa)
for(i in 1:nrow(africa)){
  if(cases[i]>0){
    stackbox(coords[i,1],coords[i,2],africa$cases[i],1,border="#606060",col="#0083FE")
  }
}

I’ve picked colours that look a bit like your original. Note that the boxes are in plot coordinates, so I had to make them 0.1 of a degree. You may wish to transform your map to a euclidean projection (using spTransform from package:gdal) and then they’ll be in those units and properly square.

Doing nice text labels like in your original would be tricky though…