Reduce space in between subplots containing choropleth maps

Question

(I posted this on Stackoverflow, but thought this may be a better venue)

I am trying to generate a figure containing six choropleth maps in R. Currently my code looks something like this:

library(rgdal)
library(GISTools)

# code that loads data needed to generate choropleth maps not shown

par(mfrow = c(3,2), mar=c(0,0,0,0), oma=c(0,6,6,0))


choropleth(mn_county, mn_county$emppct.tert.2006, shades) 
mtext( 'Secondary', side=3, line=2)
mtext( '1998', side=2, line=2)

choropleth(mn_county, mn_county$emppct.tert.2006, shades) 
# choropleth maps are repeated in this post for simplicity
mtext( 'Tertiary', side=3, line=2)

choropleth(mn_county, mn_county$emppct.tert.2006, shades)
mtext( '2006', side=2, line=2)

choropleth(mn_county, mn_county$emppct.tert.2006, shades)
choropleth(mn_county, mn_county$emppct.tert.2006, shades)
mtext( '2014', side=2, line=2)

choropleth(mn_county, mn_county$emppct.tert.2006, shades)

The problem is, even though I set margins mar to be zero throughout, there are still big gaps between the columns (see below). Not just between the choropleth maps, but also between the row headings (1998, 2006, 2014) and the maps.

How can I reduce this wide space?

P.S. I've been trying to find a GIS shapefile which I can directly pull off from the internet (I don't think I can attach shapefiles in posts), but can't find one. Any idea how I can circumvent this problem?

Answer 1

Use the choropleth example to create some sample data:

require(GISTools)
example(choropleth)

Then duplicate your work:

par(mfrow = c(3,2), mar=c(0,0,0,0), oma=c(0,6,6,0))
choropleth(sids,sids.rate,shades)
mtext( 'Secondary', side=3, line=2)
mtext( '1998', side=2, line=2)
choropleth(sids,sids.rate,shades)
mtext( 'Tertiary', side=3, line=2)
choropleth(sids,sids.rate,shades)
mtext( '2006', side=2, line=2)
choropleth(sids,sids.rate,shades)
choropleth(sids,sids.rate,shades)
mtext( '2014', side=2, line=2)
choropleth(sids,sids.rate,shades)

That gives:

But on resizing my graphics window it closes up the gaps:

Note that because of the shape of the map data here this looks best on a nearly-square graphics window, whereas your data will probably need a taller-than-wide window.