sf point object plot: fixed border color and different background colors

Question

I'm having a hard time plotting an sf point object. Basically I want to show the points with a black border and a fill color according to a variable. In base plot I would do this to impose border color with different background colors:

plot(1:3, cex = 3, pch = 21, col = 'red', bg = c('blue', 'green', 'yellow'), lwd = 2)

I use pch = 21 in order to fill the points with bg colors while using col = 'red' as the point border color.

Using a sf object I can use col to impose the border color but the legend disappears (according to the documentation for plot {sf}, if col is passed to the function the legend is suppressed).

library(sf)
# example
df <- data.frame(est = c('A', 'B', 'C'), 
             long = c(-70, -68, -69), 
             lat = c(-12.2, -12.4, -12), 
             RMSE = c(25, 8, 55)) %>% 
    st_as_sf(coords = c('long', 'lat'), crs = 4326)

# reclassifying the RMSE variable:
df$rmse_cut <- cut(df$RMSE, c(0,15,30,45,60))

# plotting the map
plot(df['rmse_cut'], main = 'RMSE', graticule = TRUE, axes = TRUE, 
bgc = 'gray92', 
pch = 21, lwd = 2, cex = 3,
col = 'black', 
bg = c('blue', 'green', 'yellow'))

But plotting without col:

plot(df['rmse_cut'], main = 'RMSE', graticule = TRUE, axes = TRUE, 
bgc = 'gray92', 
pch = 21, lwd = 2, cex = 3,
bg = c('blue', 'green', 'yellow'))

The borders are sorted by the variable rmse_cut but the background color is fixed. How can I use a single color for point borders while using background colors to show the different values from the rmse_cut variable?.

There's probably a more direct route, but you can overplot the points, first plotting the fill, then the strokes (or with different plotting characters). Or just use ggplot, which has solid sf support. — alistaire
I'll go with the ggplot2 option but I realize I have many scripts in base R. Perhaps finding a solution to this would save me some time (I think it'll take quite a lot of time to recreate my old plots with ggplot2). Anyway, thank you. — noriega

thelatemail thelatemail · Accepted Answer · 2018-08-09T04:46:48

Remember base plotting! You need to sort out your palettes so that they are consistent, and then call the palette referenced by the value:

plotpal <- sf.colors(nlevels(df[['rmse_cut']]),categorical=TRUE)
plot(df['rmse_cut'], main = 'RMSE', graticule = TRUE, axes = TRUE, bgc = 'gray92',
     type="n", pal=plotpal, key.pos=1, reset=FALSE)
plot(df[['geometry']], pch = 21, lwd = 2, cex = 3, bg=plotpal[df[['rmse_cut']]], add=TRUE)

sf point object plot: fixed border color and different background colors

2 Answers