Create a contour plot, or add contour lines to an existing plot.

`contour(x, …)`# S3 method for default
contour(x = seq(0, 1, length.out = nrow(z)),
y = seq(0, 1, length.out = ncol(z)),
z,
nlevels = 10, levels = pretty(zlim, nlevels),
labels = NULL,
xlim = range(x, finite = TRUE),
ylim = range(y, finite = TRUE),
zlim = range(z, finite = TRUE),
labcex = 0.6, drawlabels = TRUE, method = "flattest",
vfont, axes = TRUE, frame.plot = axes,
col = par("fg"), lty = par("lty"), lwd = par("lwd"),
add = FALSE, …)

x, y

locations of grid lines at which the values in `z`

are
measured. These must be in ascending order. By default, equally
spaced values from 0 to 1 are used. If `x`

is a `list`

,
its components `x$x`

and `x$y`

are used for `x`

and `y`

, respectively. If the list has component `z`

this
is used for `z`

.

z

a matrix containing the values to be plotted (`NA`

s are
allowed). Note that `x`

can be used instead of `z`

for
convenience.

nlevels

number of contour levels desired **iff**
`levels`

is not supplied.

levels

numeric vector of levels at which to draw contour lines.

labels

a vector giving the labels for the contour lines. If
`NULL`

then the levels are used as labels, otherwise this is
coerced by `as.character`

.

labcex

`cex`

for contour labelling. This is an absolute
size, not a multiple of `par("cex")`

.

drawlabels

logical. Contours are labelled if `TRUE`

.

method

character string specifying where the labels will be
located. Possible values are `"simple"`

, `"edge"`

and
`"flattest"`

(the default). See the ‘Details’ section.

vfont

if `NULL`

, the current font family and face are used
for the contour labels. If a character vector of length 2 then
Hershey vector fonts are used for the contour labels. The first
element of the vector selects a typeface and the second element
selects a fontindex (see `text`

for more information).
The default is `NULL`

on graphics devices with high-quality
rotation of text and `c("sans serif", "plain")`

otherwise.

xlim, ylim, zlim

x-, y- and z-limits for the plot.

axes, frame.plot

logical indicating whether axes or a box
should be drawn, see `plot.default`

.

col

color for the lines drawn.

lty

line type for the lines drawn.

lwd

line width for the lines drawn.

add

logical. If `TRUE`

, add to a current plot.

…

additional arguments to `plot.window`

,
`title`

, `Axis`

and `box`

,
typically graphical parameters such as `cex.axis`

.

`contour`

is a generic function with only a default method in
base R.

The methods for positioning the labels on contours are `"simple"`

(draw at the edge of the plot, overlaying the contour line),
`"edge"`

(draw at the edge of the plot, embedded in the contour
line, with no labels overlapping) and `"flattest"`

(draw on the flattest section of the contour, embedded in the
contour line, with no labels overlapping). The second and third may
not draw a label on every contour line.

For information about vector fonts, see the
help for `text`

and `Hershey`

.

Notice that `contour`

interprets the `z`

matrix as a table of
`f(x[i], y[j])`

values, so that the x axis corresponds to row
number and the y axis to column number, with column 1 at the bottom,
i.e.a 90 degree counter-clockwise rotation of the conventional textual
layout.

Alternatively, use `contourplot`

from the
lattice package where the `formula`

notation allows
to use vectors `x`

, `y`

, and `z`

of the same length.

There is limited control over the axes and frame as arguments
`col`

, `lwd`

and `lty`

refer to the contour lines
(rather than being general graphical parameters). For more control,
add contours to a plot, or add axes and frame to a contour plot.

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
*The New S Language*.
Wadsworth & Brooks/Cole.

`options("max.contour.segments")`

for the maximal
complexity of a single contour line.

`contourLines`

, `filled.contour`

for color-filled contours,
`contourplot`

(and
`levelplot`

) from package lattice.
Further, `image`

and the graphics demo which can be
invoked as `demo(graphics)`

.

# NOT RUN { require(grDevices) # for colours x <- -6:16 op <- par(mfrow = c(2, 2)) contour(outer(x, x), method = "edge", vfont = c("sans serif", "plain")) z <- outer(x, sqrt(abs(x)), FUN = "/") image(x, x, z) contour(x, x, z, col = "pink", add = TRUE, method = "edge", vfont = c("sans serif", "plain")) contour(x, x, z, ylim = c(1, 6), method = "simple", labcex = 1, xlab = quote(x[1]), ylab = quote(x[2])) contour(x, x, z, ylim = c(-6, 6), nlev = 20, lty = 2, method = "simple", main = "20 levels; \"simple\" labelling method") par(op) ## Persian Rug Art: x <- y <- seq(-4*pi, 4*pi, len = 27) r <- sqrt(outer(x^2, y^2, "+")) opar <- par(mfrow = c(2, 2), mar = rep(0, 4)) for(f in pi^(0:3)) contour(cos(r^2)*exp(-r/f), drawlabels = FALSE, axes = FALSE, frame = TRUE) rx <- range(x <- 10*1:nrow(volcano)) ry <- range(y <- 10*1:ncol(volcano)) ry <- ry + c(-1, 1) * (diff(rx) - diff(ry))/2 tcol <- terrain.colors(12) par(opar); opar <- par(pty = "s", bg = "lightcyan") plot(x = 0, y = 0, type = "n", xlim = rx, ylim = ry, xlab = "", ylab = "") u <- par("usr") rect(u[1], u[3], u[2], u[4], col = tcol[8], border = "red") contour(x, y, volcano, col = tcol[2], lty = "solid", add = TRUE, vfont = c("sans serif", "plain")) title("A Topographic Map of Maunga Whau", font = 4) abline(h = 200*0:4, v = 200*0:4, col = "lightgray", lty = 2, lwd = 0.1) ## contourLines produces the same contour lines as contour plot(x = 0, y = 0, type = "n", xlim = rx, ylim = ry, xlab = "", ylab = "") u <- par("usr") rect(u[1], u[3], u[2], u[4], col = tcol[8], border = "red") contour(x, y, volcano, col = tcol[1], lty = "solid", add = TRUE, vfont = c("sans serif", "plain")) line.list <- contourLines(x, y, volcano) invisible(lapply(line.list, lines, lwd=3, col=adjustcolor(2, .3))) par(opar) # }