[R] adding legend to choropleth map using GISTools

Martha Zorn mzorn at schoolph.umass.edu
Mon Jan 13 00:19:30 CET 2014

I am having problems with adding legend to choropleth map using GISTools.  The map that I get does not include a legend (see attached).   Thanks for any help you can provide.
Below is my code:
#read in sample
a <- matrix(at001$npovr, ncol=1)
rownames(a) <- as.character(at001$County)
##Sets working libraries for following code

##Reads in MA County shape file
#at work MAcounties<-readShapeSpatial("J:/Projects/Gambling/web/shiny/co25_d00_shp/co25_d00.shp")
sorted.a <- a[MAcounties at data[,"NAME"], 1]

shades <- auto.shading(sorted.a, n = 6, cutter = rangeCuts, cols = brewer.pal(6, "Greens"))
# Draw a map based on this scheme
# Add a legend based on this scheme
choro.legend(-82, 34.87, shades, fmt = "%4.1f", title = "Poverty Rates")
# Add a title to the map
title("Poverty Rates in Massachusetts by County")
# ... and a little more explanatory text
text(-85.3, 30.4, "Source: XXXXXX")
# and draw a box around it
box(which = "outer")
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