quilt.plot {fields}  R Documentation 
Given a vector of z values associated with 2d locations this function produces an imagelike plot where the locations are discretized to a grid and the z values are coded as a color level from a color scale.
quilt.plot(x, y, z, nrow = 64, ncol = 64, grid = NULL, add.legend=TRUE,...)
x 
A vector of the x coordinates of the locations or a a 2 column matrix of the xy coordinates. 
y 
A vector of the y coordinates or if the locations are passed in x the z vector 
z 
Values of the variable to be plotted. 
nrow 
Number of grid boxes in x. 
ncol 
Number of grid boxes in y. 
grid 
A grid in the form of a grid list . 
add.legend 

... 
arguments to be passed to the image.plot function 
This function combines the discretization to an image by the function
as.image
and is then graphed by image.plot
.
Locations that fall into the same grid box will have their z values
averaged.
A similar function exists in the lattice package. The advantage of this fields version is that it uses the standard R graphics functions and is written in R code. Also, the aggregation to average values for z values in the same gird box allows for different choices of grids. If two locations are very close, separating them could results in very small boxes.
As always, legend placement is never completely automatic. Place the
legend independently for more control, perhaps using image.plot
in tandem with split.screen
or enlarging the plot margin
See help(image.plot)
for examples of this function and these
strategies.
D.Nychka
as.image, image.plot, lattice, persp, drape.plot
data( ozone2) # plot 16 day of ozone data set quilt.plot( ozone2$lon.lat, ozone2$y[16,]) US( add=TRUE, col="grey", lwd=2) # # and ... if you are fussy # do it again # quilt.plot( ozone2$lon.lat, ozone2$y[16,],add=TRUE) # to draw over the state boundaries. # ### adding a legend strip "by hand" par( mar=c( 5,5,5,10)) # save some room for the legend quilt.plot( ozone2$lon.lat, ozone2$y[16,], add.legend=FALSE) image.plot(ozone2$lon.lat, ozone2$y[16,],legend.only=TRUE)