Custom Legend in R

map-new-legend.R

library(OIdata)
library(RColorBrewer)
library(classInt)

# load state data from OIdata package:
data(state)

# set constants:
nclr <- 8 # number of bins
min <- 0 # theoretical minimum
max <- 100 # theoretical maximum
breaks <- (max - min) / nclr

# set up colors:
plotclr <- brewer.pal(nclr, "Oranges")
plotvar <- state$coal
class <- classIntervals(plotvar,
  nclr,
  style = "fixed",
  fixedBreaks = seq(min, max, breaks))
colcode <- findColours(class, 
  plotclr)
NAColor <- "gray80"
plotclr <- c(plotclr, NAColor)

# map data:
map("state", # base
  col = NAColor,
  fill = TRUE,
  lty = 0)
map("state", # data
  col = colcode,
  fill = TRUE,
  lty = 0,
  add = TRUE)
map("state", # border
  col = "gray",
  lwd = 1.4,
  lty = 1,
  add = TRUE)

# set legend text:
legendText <- c()
for(i in seq(min, max - (max - min) / nclr, (max - min) / nclr)) {
  if (i == max(seq(min, max - (max - min) / nclr, (max - min) / nclr))) {
    legendText <- c(legendText, paste(round(i,3), "\u2264 n \u2264", round(i + (max - min) / nclr,3)))
    if (!is.na(NAColor)) legendText <- c(legendText, "NA")
  } else
    legendText <- c(legendText, paste(round(i,3), "\u2264 n <", round(i + (max - min) / nclr,3))) 
}

legend("bottomleft", # position
  legend = legendText, 
  title = "Percent",
  fill = plotclr,
  cex = 0.56,
  bty = "n") # border

map-standard-legend.R

library(OIdata)
library(RColorBrewer)
library(classInt)

# load state data from OIdata package:
data(state)

# set constants:
nclr <- 8 # number of bins
min <- 0 # theoretical minimum
max <- 100 # theoretical maximum
breaks <- (max - min) / nclr

# set up colors:
plotclr <- brewer.pal(nclr, "Oranges")
plotvar <- state$coal
class <- classIntervals(plotvar,
  nclr,
  style = "fixed",
  fixedBreaks = seq(min, max, breaks))
colcode <- findColours(class, 
  plotclr)

# map data:
map("state", # base
  col = "gray80",
  fill = TRUE,
  lty = 0)
map("state", # data
  col = colcode,
  fill = TRUE,
  lty = 0,
  add = TRUE)
map("state", # border
  col = "gray",
  lwd = 1.4,
  lty = 1,
  add = TRUE)

legend("bottomleft", # position
  legend = names(attr(colcode, "table")), 
  title = "Percent",
  fill = attr(colcode, "palette"),
  cex = 0.56,
  bty = "n") # border

sessionInfo.txt

> sessionInfo()
R version 3.0.1 (2013-05-16)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=C                 LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] classInt_0.1-21    RColorBrewer_1.0-5 OIdata_1.0         maps_2.3-6        
[5] RCurl_1.95-4.1     bitops_1.0-6      

loaded via a namespace (and not attached):
[1] class_7.3-9 e1071_1.6-1 tools_3.0.1