## make sure poisonoak1.txt is in R's working directory
install.packages("maps")
library(maps)
library(help=maps)
install.packages("maptools")
library(maptools)
x = scan("poisonoak1.txt",skip=1)

lat = x[(1:84)*2-1]
lon = x[(1:84)*2]
map("county", c("california"))
## help(map)
map.axes()
map("county", c("california,los angeles"))
map.axes()
points(lon,lat,cex=.5)
mtext(s=3,"Poison oak sightings in LA County \n according to calflora.org Sept 2009")
## binsize = .1 degree in both lon and lat
x1 = matrix(0,nrow=14,ncol=10)
for(i in 1:14){
    for(j in 1:10){
	x1[i,j] = sum((lon < -119 + .1*i) & (lon > -119.1 + .1*i - .001) & 
	    (lat < 33.7 + .1*j) & (lat > 33.6 + .1*j - .001))
    }
}
par(mfrow=c(1,2))
map("county", c("california,los angeles"))
map.axes()
image(-119+c(1:14)*.1-.05,33.7+c(1:10)*.1-.05,x1,add=T,col=gray((64:20)/64))
points(lon,lat,cex=.5)
map("county", c("california,los angeles"),add=T)
## now add a legend
zmin = min(x1)
zmax = max(x1)
zrng = zmax-zmin
zmid = zmin+zrng/2
zgrid = seq(zmin,zmax,length=100)
plot(c(0,10), c(zmid-2*zrng/3,zmid+2*zrng/3), type="n", axes=F, xlab="",
ylab="")
image(c(-1:1), zgrid, matrix(rep(zgrid,2), ncol=100, byrow=T), add=T,
col=gray((64:20)/64))
text(2.5, zmin, as.character(signif(zmin,2)), cex=1)
text(2.5, zmax, as.character(signif(zmax,2)), cex=1)
text(2.5, zmid, as.character(signif(zmid,2)), cex=1)
text(4.5, zmid, "Values", srt=-90)