Scatter Plots - R Graphics - page 111

the low and high colors. By default, the legend doesn't show an entry for the lowest values. This
is because the range of the color scale starts not from zero, but from the smallest nonzero quant-
ity in a bin—probably 1, in this case. To make the legend show a zero (as in Figure 5-14 , right),
we can manually set the range from 0 to the maximum, 6000, using limits ( Figure 5-14 , left):
sp + stat_bin2d()
sp + stat_bin2d(bins = 50 ) +
scale_fill_gradient(low = "lightblue" , high = "red" , limits = c( 0 , 6000 ))
Figure 5-14. Left: binning data with stat_bin2d(); right: with more bins, manually specified colors,
and legend breaks
Another alternative is to bin the data into hexagons instead of rectangles, with stat_binhex()
( Figure 5-15 ) . It works just like stat_bin2d() . To use it, you must first install the hexbin pack-
age, with install.packages("hexbin") :
library(hexbin)
sp + stat_binhex() +
scale_fill_gradient(low = "lightblue" , high = "red" ,
limits = c( 0 , 8000 ))
sp + stat_binhex() +
scale_fill_gradient(low = "lightblue" , high = "red" ,
breaks = c( 0 , 250 , 500 , 1000 , 2000 , 4000 , 6000 ),
limits = c( 0 , 6000 ))