.BG
.FN contour
.TL
Contour Plot
.CS
contour(x, y, z, v, nint=5, add=FALSE, labex)
.AG x
vector containing \f2x\fP coordinates of grid over which `z' is
evaluated.
.AG y
vector of grid \f2y\fP coordinates.
.AG z
matrix `length(x)' by `length(y)' giving surface height at grid
points, i.e., `z[i,j]' is evaluated at `x[i]', `y[j]'.
The `rows' of `z' are indexed by `x', and the `columns' by `y'.
Missing values (`NA's) are allowed.
.AG v
vector of heights of contour lines.  By default,
approximately `nint' lines are drawn which cover most of the
range of `z'.  See the function `pretty'.
.AG nint=
the approximate number of contour intervals desired.
Not needed if `v' is specified.
.AG add=
flag which if `TRUE' causes contour lines to be added to the
current plot. Useful for adding contours with different
`labex' parameter, line type, etc.
.AG labex=
the desired size of the labels on contour lines. By default the
current character size is used.  If `labex' is 0,
no labels are plotted on contours.
.PP
The first argument may be a list, `xyz', say.
Components `xyz$x', `xyz$y' and `xyz$z' will be used.  In particular, the
result of `interp' is suitable as an argument to `contour'.
.GR
.Tl
.SA
`interp', `persp'.
.EX
rx<-range(ozone.xy$x)
ry<-range(ozone.xy$y)
usa(xlim=rx,ylim=ry,lty=2,col=2)
i<-interp(ozone.xy$x,ozone.xy$y,ozone.median)
contour(i,add=T,labex=0)
text(ozone.xy,ozone.median)
title(main="Median Ozone Concentrations in the North East")
.PI 4i
.KW multivariate
.KW aplot
.KW hplot
.WR
